Lectures on human and animal psychology

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HUMAN AND ANIMAL
PSYCHOLOGY

BY

WILHELM WUNDT

PROFESSOR OF PHILOSOPHY AT THE UNIVERSITY OF LEIPZIG

Translated from the Second German Edition

BY

J. E. CREIGHTON & E. B. TITCHENER

LONDON

SWAN SONNENSCHEIN & CO., LIM.

NEW YO^K: THE MACMILLAN CO.

1907

15 o

FIRST EDITION, October, 1894.
SECOND EDITION, June, 1896.
THIRD EDITION, November igoi,
FOURTH EDITION, August, 1907.

4?
ILL
A/

TRANSLATORS' PREFACE

6 i

THE present volume is the first of Professor Wundt's
writings to be made generally accessible to the English-
speaking public. Its comparatively popular and intro-
ductory character will, it is hoped, render it especially accept-
able both to those beginning the study of psychology, to whom
the technicalities of the author's Grundzuge would present very
considerable difficulties, and to workers in other departments of
science who may desire some knowledge of the methods and
results of the new psychological movement.

The translators have endeavoured throughout to retain the
oral form of the original Lectures. They have aimed, at the
same time, to furnish a literal, as distinguished from a verbal,
rendering of the German text. In view of the confusion which
still obtains in English psychological terminology, they have
attempted a precise use of words even at the occasional cost of
literary effect. No word or phrase, however, has been em-
ployed which has not already received the sanction of well-known
psychological writers.

J. E. CREIGHTON.
E. B. TITCHENER.

CORNELL UNIVERSITY, ITHACA, N.Y.

211262.

TRANSLATORS' PREFACE TO SECOND
EDITION.

ri"1 HE Translators have made but few changes, and those of

minor importance, in the text of this edition. The

system of nomenclature adopted in the first issue of the

work has met with general approval, and therefore remains

unchanged. A few words and phrases have been altered, here

and there, in the interests of greater clearness and precision ;

and an index of names and subjects has been added.

CORNELL UNIVERSITY, ITHACA, N.Y.
I5th April, 1896.

AUTHOR'S PREFACE TO SECOND
EDITION

WHEN I was asked some years since by the publisher of
this work to undertake its revision, I felt some hesita-
tion in complying with his request. The first edition
of the Lectures appeared thirty years ago ; and during that
time there had not only been a great advance in experimental
psychology, but my own scientific knowledge and convictions
had been considerably increased and modified. Thirty years
ago the science was no more than a programme for the future.
Except in psychophysics, where Fechner had just broken
ground, everything remained still to do ; and distrust and sus-
picion met the investigator at every turn. As for myself, I had
had but little experience in the difficult work of psychological
analysis, which the gradual development of the experimental
methods has done so much to further ; and set about my task
with more zeal than discretion. So that for years before the
appearance of the first edition of my Physiological Psychology,
in which I took up the same problem with more modesty and
caution, I had learned to look upon the Lectures as wild oats
of my youthful days, which I would gladly have forgotten.
But, unfortunately, hypotheses and views represented in them
would every now and again be confused with or counted among
my more mature convictions.

That I have resolved to undertake a- second edition despite
these somewhat discouraging facts, and in preference to the
more grateful task of writing a new work of similar character,,
is due in the main to two circumstances. In the first place, I

vi Author s Preface to Second Edition

thought that, though the original volumes were defective both in
general execution and in many points of detail, still a certain
number of their chapters might stand unchanged, while I
should perhaps be unable to attain again the freshness and
force which characterised the first expression of my views.
Secondly, every statement in the former edition about which I
had modified or abandoned my original opinion seemed to lay
upon me an obligation which I would fain discharge to the
limit of my ability. Nevertheless, I will not omit in this place
the express declaration that I no longer recognise as mine any
view formulated in the earlier edition which is not admitted into
the present. The elimination of everything that more recent
inquiry had superseded has considerably diminished the size ol
the work. It has also suffered curtailment by the total exclu-
sion of the discussions of social psychology which occupied a
large portion of the second volume of the original book. It has
been a matter of principle with me to restrict the contents of
the Lectures to the individual psychology of man and the
animals. As a matter of fact, the amount of material which
social psychology has at its disposal is now so great, and the
position of the science with regard to the points discussed has
undergone so radical a change, that revision of the old chapters
would necessarily mean rewriting. But within the prescribed
limits, I have adhered to my former plan of not attempting any
completeness of exposition, but rather of taking full advantage
of the lecture form and confining myself to the treatment of
topics which I thought especially characteristic of the spirit
and trend of modern psychology. At the same time, it seemed
permissible to make the work in some sense supplementary to
my other writings by devoting few words to subjects which I
have elsewhere discussed in detail, and giving more attention to
topics which are less prominent, particularly in my Physiologi-
cal Psychology. Thus I have based the discussion of Weber's
law entirely upon the method of just noticeable differences,
although this is the most imperfect of the measurement-methods
-and would hardly now be employed in investigations which

Author 's Preface to Second Edition vii

made any claim to scientific accuracy. Again, in developing
the theory of spatial localisation I have retained my previous
plan of elucidating its much-misunderstood fundamental con-
ceptions, and of the sensations attaching to movement have
only dealt with muscle-sensations, although the rdle of certain
complexes of pressure-sensations in the surrounding parts is
really not less important. The reader who desires a deeper
insight into psychology will, I hope, not omit to refer in such
cases to my more systematic work, which is more especially
devoted to the investigation of the physiological correlates of
psychical processes.

The first edition of these Lectures was principally based upon
Fechner's Psychophysik and my own Beitrdge zur Theorie der
Sinneswahrnehmungen, which appeared between 18*58 and 1862.
The lectures dealing with these subjects have undergone the
least alteration in the second edition. I may perhaps be also
allowed to state that the treatment of the problem of the
causality of will in Lecture XXIX. stands for the most part
precisely as it did in my previous exposition. The following
lectures of the second edition present portions of the older work
in revised form: — I. (I., II., of the former edition), II. (VII.), III.
(VIII.), IV. (IX.), VIII. (XIV.), IX. (XV.), X., XI. (XVI.,
XVII.), XII. (XXL), XIII. (XXII.), XXIX. (LV., LVI.) ;
entirely rewritten are— V. (XL), VI. (X.), VII. (XIII.), XIV.
(XXX.), XXV. (XXXI.), XXVI. (LI., LIL), XXVIII. (XLII.) ;
new are :— XV., XVL, XVIL, XVIIL, XIX., XX., XXL,
XXIL, XXIIL, XXIV., XXVIL, XXX. Very little of the
lectures of the first edition not quoted here has been included in
the present volume.

W. WUNDT.
LEIPZIG, Aptil, 1892.

CONTENTS.

PAGE

LECTURE FIRST i-ii

Philosophical Anticipations of Psychology, 1-5. Spiritualism
and Materialism, 5-7. Methods and Aids of Psychological
Investigation, 7-11.

LECTURE SECOND 12-32

Analysis of Mental Processes, 12-15. Idea and Sensation, 15-17.
Intensity and Quality of Sensation, 17, 18. Measurement of
the Intensity of Sensation, 18-32.

LECTURE THIRD 33-49

Estimation of the Intensity of Sensation, 33-39. Mathematical
Expression of the Law of Sensation-intensities, 39-42. Signi-
ficance of Negative Sensation-values, 42-47. Unit of Stimulus
and Unit of Sensation, 47-49.

LECTURE FOURTH 50-63

A Just Noticeable Sensation, 50-56. Upper and Lower Limit of
Weber's Law, 56-59. Psychological Interpretation of the
Law, 59-63.

LECTURE FIFTH 64-86

Quality of Sensation, 64-66. Tone-sensations ; Beats, 67-73.
Clang-colour, 73-75. Simultaneous Clangs, 75-77. Noises,
77, 78. Measurement of Differences of Tone-sensations, 78-81.
The Tonal Scale, 81-84. Relation to Weber's Law, 84-86.

LECTURE SIXTH 87-107

Light-sensations ; Sensations of Colour and Brightness, 87, 88.
Analysis and Mixture of Colours, 88-95. The Three Primary
Colours, 96-98. Leonardo's Four Principal Colours, 99-103.
Theory of Light-sensations, 103-107.

LECTURE SEVENTH 108-119

Relation of the Senses of Sight and Hearing, 108. Positive and
Negative After-images, 108-110. Mechanical and Chemical
Senses, no, in. Phenomena of Contrast, in-ii8. General
Law of Relativity, 118, 119.

LECTURE EIGHTH 120-133

Reflex Movements, 120-126. Purposiveness of the Reflex,
126-128. Development of the Reflexes of Touch and Sight,
128-133.

LECTURE NINTH 134-148

Muscle-sensations : their Influence upon Localisation, 134-138.
Connexion of Sensations of Movement with other Sensations,
138-142. Influence of Practice upon Reflex Movements,

Contents

143-145. Arrangement in Space a Process of Association,
145-148.

LECTURE TENTH 149-169

Influence of Ocular Movement on Spatial Vision, 149-156. Geo-
metrical Optical Illusions, 156, 157. Spatial Perceptions of the
Sense of Touch, 157-160. Accidental and Congenital Blind-
ness, 161-163. Why are not Visual Objects Inverted? 163-167.
Concluding Remarks upon the Theory of Space-construction,
167-169.

LECTURE ELEVENTH 170-181

The Separation of Visual Ideas; Influence of Boundary Lines,
170-172. Ideas of Depth, 172-176. Relations between
Apparent Magnitude and Distance of Objects, 176-181.

LECTURE TWELFTH 182-194

Binocular Vision ; Difference of the Two Retinal Images, 182-186.
The Stereoscope ; Simplest Stereoscopic Experiments, 186-190.
Theory of Stereoscopic Vision, 190-194.

LECTURE THIRTEENTH 195-209

Combination of Similar Stereoscopic Images, 195-197. Idea-
tional Change in Stereoscopic Combination, 197-199. Reflec-
tion and Lustre ; Theory of Lustre, 199-205. Phenomena of
Suppression in Binocular Vision, 205-209.

LECTURE FOURTEENTH 210-222

The Feelings, 210-213. Sense-feelings, 213-217. Common
Feeling and the other Total Feelings, 217-221. Relation of
Feeling to Idea, 221, 222.

LECTURE FIFTEENTH 223-234

Relation of Feeling to Will ; Impulse and Desire, 223, 224.
Development of Will, 224-228. Simple and Complex Volun-
tary Acts, 228-233. Psychological Elements in Voluntary
Action, 233, 234.

LECTURE SIXTEENTH 235-251

The Concept of Consciousness, 235-239. Condition of Ideas in
Consciousness, 239-243. Perception and Apperception ; Clear-
ness and Distinctness of Ideas, 244-247. Phenomena accom-
panying Apperception, 247,248. Attention, 249,250. Self-
consciousness, 250, 251.

LECTURE SEVENTEENTH 252-265

Development of Attention ; Passive and Active Apperception,
252-255. Attention and Will ; Fluctuations of Attention,
256-258. Range of Consciousness : Formation and Division
of Rhythmical Series, 258-265.

LECTURE EIGHTEENTH 266-281

Temporal Course of Ideas, 266, 267. Personal Difference of
Astronomers : Eye and Ear Method, 267-271. Method of
Registration, 272-276. Reaction-time, 276-278. Temporal
Determination of Mental Processes, 278-281.

LECTURE NINETEENTH . . 282-294

Qualitative Change of Ideas, 282-283. Association of Ideas ;
Simultaneous Association ; Complication, 283-286. Assimi-
lation, 286-290. Theory of Simultaneous Association, 290-294.

Contents

PAGE

LECTURE TWENTIETH 295-307

Successive Associations, 295-297. Association by Similarity
and Contiguity, 297. Cognition and Recognition as Simple
Forms of Association, 298-303. Theory of Successive Associa-
tions, 304-306. Indirect Association, 306, 307.

LECTURE TWENTY- FIRST 308-322

Concepts and Judgments, 308-311. Distinguishing Marks of
Intellectual Processes, 312-314. Development of the Intellec-
tual Functions, 314-316. Mental Derangement, 316-322.

LECTURE TWENTY-SECOND 323-339

Dreams, 323-327. Sleep-walking, 327, 328. Hypnotism and
Suggestion, 328-335. Auto-suggestion and Post-hypnotic In-
fluence, 335-337. Errors of the ' Hypnotism-psychology,'
337-339-

LECTURE TWENTY-THIRD 340-352-"

Problems of Animal Psychology ; Deficiencies of the Science,
340-345. Methodological Rules, 345, 346. Acts of Cognition
and Recognition among Animals, 347-350. Association among
the Lower Animals, 350-352.

LECTURE TWENTY-FOURTH 353-366

Mentality of the Higher Animals, 353-357. Animal Play, 357,
358. Alleged Formation of Judgments and Concepts, 358-36*.
General Significance of Association, 362-364. Man and the
.Animals, 364-366.

LECTURE TWENTY-FIFTH 367-380-

Connexion of Affective States in Consciousness, 367-369. Sen-
sory Accompaniments of Compound Feelings, 370,371.
Emotion, 371-377. Intellectual Feelings, 378-380.

LECTURE TWENTY-SIXTH 381-394

Expression of the Emotions, 381-385. Impulsive and Volitional
Action, 385-388. Instinctive Action, 388, 389. Theories of
Instinct, 389-394.

LECTURE TWENTY-SEVENTH 395-410

Instinctive Action in Man, 395-397. Acquired Instincts, 397-399.
Connate Instincts, 399-401. Practice, Imitation, and Inherit-
ance, 402-406. Relation of Animal to Human Instinct,
406-410.

LECTURE TWENTY-EIGHTH 411-422

Social Instincts ; Temporary Associations and Friendships of
Animals, 411. Animal Marriage, 412,413. Animal Societies
and States, 414-422.

LECTURE TWENTY-NINTH 423-436

Voluntary Action, 423, 424. The Causality of Will, 424-428.
Relation of the Individual to the General Will, 428-432.
Character as the Ultimate Cause of Will, 432-436.

LECTURE THIRTIETH 437-454

Concluding Remarks ; The Question of Immortality, 437-440.
The Principle of Psychophysical Parallelism, 440-445. Old
and New Phrenology, 445-448. The Empirical Significance
of the Principle of Parallelism, 448-451. The Nature of Mind,
451-454.

LECTURE I

§ I. PHILOSOPHICAL ANTICIPATIONS OF PSYCHOLOGY. § II. SPIRITUAL-
ISM AND MATERIALISM. § III. METHODS AND AIDS OF PSYCHO-
LOGICAL INVESTIGATION.

PSYCHOLOGY, even in our own day, shows more clearly
than any other experiential science traces of the con-
flict of philosophical systems. We may regret this influence
in the interest of psychological investigation, because it has
been the chief obstacle in the way of an impartial examination
of mental life. But in the light of history we see that it was
inevitable. Natural science has gradually taken shape from a
natural philosophy which paved the way for it, and the effects
of which may still be recognised in current scientific theory.
That these effects are more fundamental and more permanent
in the case of psychology is intelligible when we consider the
problem which is set before it. Psychology has to investigate
that which we call internal experience, — i.e., our own sensation
and feeling, our thought and volition, — in contradistinction to the
objects of external experience, which form the subject matter
of natural science. Man himself, not as he appears from with-
out, but as he is in his own immediate experience, is the real
problem of psychology. Whatever else is included in the circle
of psychological discussion, — the mental life of animals, the
common ideas and actions of mankind which spring from simi-
larity of mental nature, and the mental achievements of the
individual or of society, — all this has reference to the one
original problem, however much our understanding of mental
life be widened and deepened by the consideration of it. But
the questions with which psychology thus comes into contact
are at the same time problems for philosophy. And philosophy

B

2 Lectures on Human and Animal Psychology

had made various attempts to solve them long before psycho-
logy as an experiential science had come into being.

The psychology of to-day, then, neither wishes to deny to
philosophy its right to occupy itself with these matters, nor is
able to dispute the close connection of philosophical and psy-
chological problems. But in one respect it has undergone a
radical change of standpoint It refuses to regard psychological
investigation as in any sense dependent upon foregone meta-
physical conclusions. It would rather reverse the relation of
psychology to philosophy, just as empirical natural science long
ago reversed its relation to natural philosophy, — in so far, that
is, as it rejected all philosophic speculations which were not
based upon experience. Instead of a psychology founded upon
philosophical presuppositions, we require a philosophy to whose
speculations value is ascribed only so long as they pay regard
at every step to the facts of psychological, as well as to those
of scientific, experience.

It will, therefore, be a matter of principle for us in these lec-
tures to stand apart from the strife of philosophic systems. But
since the thought of to-day is subjected on all sides to the in-
fluence of a philosophic past which counts its years by thou-
sands, and since the concepts and general notions under which
an undifferentiated philosophy arranged the facts of mental life
have become part of the general educated consciousness, and
have never ceased to hinder the unprejudiced consideration of
things as they are, it is our bounden duty to characterise and
justify the standpoint which we propose to adopt. We will,
therefore, first of all glance for a moment at the history of
philosophy before the appearance of psychology.

In the beginnings of reflective thought, the perception of the
external world preponderates over the internal experience of
idea and thought, of feeling and will. The earliest psychology
is therefore Materialism : the mind is air, or fire, or ether, —
always some form of matter, however attenuated this matter
may become in the effort to dematerialise it. Plato was the
first among the Greeks to separate mind from body. Mind he
regarded as the ruling principle of the body. And this separa-
tion paved the way for the future one-sided dualism which con-
sidered sensible existence as the obscuring and debasing of an

Philosophical Anticipations of Psychology 3

ideal, purely mental being. Aristotle, who combined with the
gift of speculation a marvellous keenness of observation, at-
tempted to harmonise these opposites by regarding mind as the
principle which vitalises and informs matter. He saw the
direct operation of mental powers in the forms of animals, in
the expression of the human figure at rest and in movement,
even in the processes of growth and nutrition. And he gene-
ralised all this in his conclusion that mind is the creator of all
organic form, working upon matter as the sculptor works on
marble. Life and mentality were for him identical terms ;
even the vegetable world was on his theory endowed with
mind. But, apart from this, Aristotle penetrated more deeply
than any of his predecessors into the facts of mental experience.
In his work upon the mind, the first in which psychology was
ever treated as an independent science, he sharply separates
from one another the fundamental mental activities ; and, so
far as the knowledge of his time allowed, sets forth their causal
connections.

The Middle Ages were wholly dominated by the Aristotelian
psychology, and more especially by its basal proposition that
mind is the principle of life. But with the dawn of the modern
period begins in psychology, as elsewhere, the return to
Platonism. Another influence combined with this to displace
Aristotelianism ; namely, the development of modern natural
science and the mechanical metaphysics which this develop-
ment brought with it. The result of these influences was the
origin of two psychological schools, which have disputed with
one another down to the present day, — Spiritualism and
Materialism. It is a curious fact that the thought of a single
man has been of primary importance in the development of
both these standpoints. Descartes, the mathematician and
philosopher, had defined mind, in opposition to Aristotle, as
exclusively thinking substance ; and following Plato, he ascribed
to it an original existence apart from the body, whence it has
received in permanent possession all those ideas which transcend
the bounds of sensible experience. This mind, in itself unspatial,
he connected with the body at one point in the brain, where it
was affected by processes in the external world, and in its turn
exercised influence upon the body.

4 Lectitres on Human and Animal Psychology

Later Spiritualism has not extended its views far beyond
these limits. It is true that Leibniz, whose doctrine of monads
regarded all existence as an ascending series of mental forces,
attempted to substitute for the Cartesian mind-substance a more
general principle, approximating once more to the Aristotelian
concept of mind. But his successor Christian Wolff returned to
the Cartesian dualism. Wolff is the originator of the so-called
theory of mental faculties, which has influenced psychology
down to the present day. This theory, based upon a superficial
classification of mental processes, was couched in terms of a
number of general notions, — memory, imagination, sensibility,
understanding, etc., — which it regarded as simple and funda-
mental forces of mind. It was left for Herbart, one of the
acutest thinkers of our century, to give a convincing proof of the
utter emptiness of this ' theory.' Herbart is at the same time
the last great representative of that modern Spiritualism which
began with Descartes. For the works of Kant and of the other
philosophers who came after him, — Fichte, Schelling, and Hegel,
— belong to a different sphere. In Herbart we still find the
concept of a simple mind-substance, which Descartes introduced
into modern philosophy, but pushed to its extreme logical
conclusion, and at the same time modified by the first principles
of Leibniz' monadology. And the consistency of this final
representative of speculative psychology makes it all the more
plain that any attempt to derive the facts of mental life from
the notion of a simple mind and its relation to other existences
different from or similar to itself must be vain and fruitless.
Think what lasting service Herbart might have done psychology,
endowed as he was in exceptional measure with the power of
analysing subjective perception, had he not expended the best
part of his ingenuity in the elaboration of that wholly imaginary
mechanics of ideation, to which his metaphysical presuppositions
led him. Still, just because he carried the concept of a simple
mind-substance to its logical conclusion, we may perhaps ascribe
to his psychology, besides its positive merits, this negative value,
— that it showed as clearly as could be the barrenness of
Spiritualism. All that is permanent in Herbart's psychological
works we owe to his capacity of accurate observation of mental
fact ; all that is untenable and mistaken proceeds from his

Spiritualism and Materialism 5

metaphysical concept of mind and the secondary hypotheses
which it compelled him to set up. So that the achievements
of this great Spiritualist show most plainly that the path which
he travelled, apart from all the contradictions into which it led
him, cannot ever be the right road for psychology. This notion
of a simple mental substance was not reached by analysis of
mental phenomena, but was superimposed upon them from
without. To assure the pre-existence and immortality of the
soul, and (secondarily) to conform in the most direct way with
the logical principle that the complex presupposes the simple,
it seemed necessary to posit an indestructible and therefore
absolutely simple and unalterable mind-atom. It was then the
business of psychological experience to reconcile itself with this
idea as best it might.

When Descartes denied mind to animals, on the ground that
the essence of mind consists in thought, and man is the only
thinking being, he cou'd have little imagined that this proposi-
tion would do as much as the strictly mechanical views which
he represented in natural philosophy to further the doctrines
which are the direct opposite of the Spiritualism which he
taught, — the doctrines of modern Materialism. If animals are
natural automata, and if all the phenomena which general
belief refers to sensation, feeling, and will are the result of purely
mechanical conditions, why should not the same explanation
hold of man ? This was the obvious inference which the
Materialism of the seventeenth and eighteenth centuries drew
from Descartes' principles.

The nai've Materialism with which philosophy began had
simply ascribed some kind of corporeality to mental existence.
But this modern Materialism took as its first principles
physiological hypotheses ; thought, sense, and idea are
physiological functions of certain organs within the nervous
system. Observation of the facts of consciousness is of no avail
until these are derived from chemical and physical processes.
Thought is simply a result of brain activity. Since this activity
•ceases when circulation is arrested and life departs, thought is

6 Lectures on Human and Animal Psychology

nothing more than a function of the substances of which the
brain, is composed.

More particularly were the scientific investigators and
physicians of the time inclined, by the character of their pursuits,
to accept this explanation of mental life in terms of what seemed
to them intelligible scientific facts. The Materialism of to-day
has made no great advance in this or in any other direction upon
the views promulgated in the last century, e.g. by de la Mettrie,
and developed by Helvetius, Holbach, and others. But this
equating of mental process and brain function, which makes
psychology a department of cerebral physiology, and therefore
a part of a general atomic mechanics, sins against the very
first rule of scientific logic, — that only those connections of facts
may be regarded as causal which obtain between generically
similar phenomena. Our feelings, thoughts, and volitions cannot
be made objects of sensible perception. We can hear the word
which expresses the thought, we can see the man who has
thought it, we can dissect the brain in which it arose ; but the
word, the man, and the brain are not the thought. And the
blood which circulates in the brain, the chemical changes which
take place there, are wholly different from the act of thought
itself.

Materialism, it is true, does not assert that these are the
thought, but that they form it. As the liver secretes bile, as the
muscle exerts motor force, so do blood and brain, heat and
electrolysis, produce idea and thought. But surely there is no
small difference between the two cases. We can prove that bile
arises in the liver by chemical processes which we are able, in
part at least, to follow out in detail. We can show, too, that
movement is produced in muscles by definite processes, which
are again the immediate result of chemical transformation. But
cerebral processes give us no shadow of indication as to how our
mental life comes into being. For the two series of phenomena
are not comparable. We can conceive how one motion may be
transformed into another, perhaps also how one sensation or
feeling is transformed into a second. But no system of cosmic
mechanics can make plain to us how a motion can pass over into
a sensation or feeling.

At the same time modern Materialism pointed out a more

Methods and Aids of Psychological Investigation 7

legitimate method of research. There are numerous experiences
which put beyond all doubt the connection of physiological
cerebral function on the one hand and of mental activity on the
other. And to investigate this connection by means of experi-
ment and observation is assuredly a task worth undertaking.
But we do not find that Materialism, even in this connection, has
made a single noteworthy contribution to our positive knowledge.
It has been content to set up baseless hypotheses regarding the
dependence of mental function upon physical process ; or it has
been concerned to refer the nature of mental forces to some
known physical agency. No analogy has been too halting, no
hypothesis too visionary, for its purpose. It was for some time
a matter of dispute whether the mental force had more resem-
blance to light or to electricity. Only on one point was there
general agreement, — that it was not ponderable.

In our day the conflict between Materialism and Spiritualism,
which was raging in the middle of the century, has almost worn
itself out. It has left behind it nothing of value for science ; and
that will not surprise any one who is acquainted with its details.
For the clash of opinion was centred once more round the old
point : in the questions concerning mind, the seat of mind, and
its connection with body. Materialism had made the very same
mistake which we have charged to the spiritualistic philosophy.
Instead of plunging boldly into the phenomena which are pre-
sented to our observation and investigating the uniformities of
their relation, it busied itself with metaphysical questions, an
answer to which, if we may expect it at all, can only be based
upon an absolutely impartial consideration of experience, which
refuses to be bound at the outset by any metaphysical
hypothesis.

§ HI

We find, then, that Materialism and Spiritualism, which set
out from such different postulates, converge in their final result.
The most obvious reason of this is their common methodological
error. The belief that it was possible to establish a science of
mental experience in terms of speculation, and the thought that
a chemical and physical investigation of the brain must be the

8 Lectures on Human ana Animal Psychology

first step towards a scientific psychology led alike to mistakes
in method. The doctrine of mind must be primarily regarded
as an experiential science. Were this otherwise, we should not
be able so much as to state a psychological problem. The
standpoint of exclusive speculation is, therefore, as unjustifiable
in psychology as it is in any science. But more than this, so
soon as we take our stand upon the ground of experience, we
have to begin our science, not with the investigation of those
experiences which refer primarily only to objects more or less
closely connected with mind, but with the direct examination ot
mind itself, — that is, of the phenomena from which its existence
was long ago inferred, and which formed the original incentive
to psychological study. The history of the science shows us
that mind and the principal mental functions were distinguished
before there was any idea that these functions were connectec
with the brain. It was not any doubt as to the purpose of this
organ which led to the abstraction which lies at the foundation
of the doctrine of mind, but simply observation of mental
phenomena. Sense, feeling, idea, and will seemed to be related
activities ; and they appeared, further, to be bound together by
the unity of self-consciousness. The mental processes began,
therefore, to be looked upon as the actions of a single being.
But since these actions were found again to be intimately
connected with bodily functions, there necessarily arose the
question of assigning to mind a seat within the body, whether
in the heart, or the brain, or any other organ. It was reserved
for later investigation to show that the brain is the sole organ
which really stands in close connection with the mental life.

But if it be sensation, feeling, idea, and will which led in
the first instance to the assumption of mind, the only natural
method of psychological investigation will be that which begins
with just these facts. First of all we must understand their
empirical nature, and then go on to reflect upon them. For it
is experience and reflection which constitute each and every
science. Experience comes first ; it gives us our bricks : reflec-
tion is the mortar, which holds the bricks together. We cannot
build without both. Reflection apart from experience and ex-
perience without reflection are alike powerless. It is therefore
essential for scientific progress that the sphere of experience be

Methods and Aids of Psychological Investigation 9

•enlarged, and new instruments of reflection from time to time
invented.

But how is it possible to extend our experience of sensations,
feelings, and thoughts ? Did not mankind feel and think
thousands of years ago, as it feels and thinks to-day ? It does,
indeed, seem as though our observation of what goes on in the
mind could never extend beyond the circle to which our own
consciousness confines it. But appearances are deceptive. Long
ago the step was taken which raised the science of psychology
above the level of this its first beginning, and extended its
horizon almost indefinitely. History, dealing with the expe-
rience of all times, has furnished us with a picture in the large
•of the character, the impulses, and the passions of mankind.
More especially is it the study of language and linguistic de-
velopment, of mythology and the history of religion and custom,
which has approached more and more closely, as historical
knowledge has increased, to the standpoint of psychological
inquiry.

The belief that our observation is confined to the brief span
of our individual life, with its scanty experience, was one of the
greatest obstacles to psychological progress in the days of the
earlier empiricism. And the opening up of the rich mines of
experience to which social psychology gives us access, for the
extension of our own subjective perceptions, is an event of
importance and of promise for the whole circle of the mental
sciences. Nor is that all. A second fact, of still greater import
for the solution of the simplest and therefore, most general
psychological problems, is the attempt that has been made to
discover new methods of observation. One new method has
been found ; it is that of experiment, which, though it revolu-
tionized the natural sciences, had not up to quite recent times
found application in psychology. When the scientific inves-
tigator is inquiring into the causes of a phenomenon, he does
not confine himself to the investigation of things as they are
given in ordinary perception. That would never take him to
his goal, though he had at his command the experiences of all
time. Thunderstorms have been recorded, indeed carefully
described, since the first beginnings of history : but what a
storm was could not be explained until the phenomena of

io Lectures on Human and Animal Psychology

electricity had become familiar, until electrical machines had
been constructed and experiments made with them. Then the
matter was easy. For when once the effects of a storm had
been observed and compared with the effect of an electric
spark, the inference was plain that the discharge of the machine
was simply a storm in miniature. What the observation of a
thousand years had left unexplained was understood in the
light of a single experiment. Even astronomy, a science which
we might think must of its very nature be confined to observa-
tion, is in its more recent development founded in a certain
sense upon experiment. So long as mere observations were
taken, the general opinion that the earth was fixed, and that
the sun and stars moved round it, could not be overthrown. It
is true that there were many phenomena which made against
this belief ; but simple observation could not furnish means for
the attainment of a better explanation. Then came Copernicus,
with the thought : ' Suppose I stand upon the sun ! ' and
henceforth it was the earth that moved, and not the sun ; the
contradictions of the old theory disappeared, and the new
system of the universe had come into being. But it was an
experiment that had led to this, though an experiment of
thought. Observation still tells us that the earth is fixed, and
the sun moving ; and if the opposite view is to become clear,
we must just repeat the Copernican experiment, and take our
stand upon the sun.

It is experiment, then, that has been the source of the
decided advance in natural science, and brought about such
revolutions in our scientific views. Let us now apply experi-
ment to the science of mind. We must remember that in every
department of investigation the experimental method takes on
an especial form, according to the nature of the facts investi-
gated. In psychology we find that only those mental pheno-
mena which are directly accessible to physical influences can
be made the subject matter of experiment. We cannot experi-
ment upon mind itself, but only upon its outworks, the organs
of sense and movement which are functionally related to mental
processes. 3o~^l§i--?y-?rZ--P.?ychQ]o^cal^jSLXperiment is at th
same time physiological, just as there are physical processes
corresponding to the mental processes of sensation, idea, and

Methods and Aids of Psychological Investigation 1 1

_wiiL— . This is, of course, no reason for denying to experiment
the character of a psychological method. It is simply due to
the general conditions of our mental life, one aspect of which is
its constant connection with the body.

The following lectures are intended as an introduction to
psychology. They do not attempt any exhaustive exposition
of the methods and results of experimental psychological inves-
tigation. That would have to assume previous knowledge
which cannot here be presupposed. Neither shall we include
in the range of our discussion the facts of social psychology,,
whose contents is extensive enough to demand an independent
treatise. We shall confine ourselves to the mental life of the
individual ; and within those limits it will be the human mind
to which we shall for the most part devote ourselves. At the
same time it appears desirable, for the right understanding of
individual mental development, that we should now and again
institute a brief comparison with the mental life of animals.

LECTURE II

:§ I. ANALYSIS OF MENTAL PROCESSES. § II. IDEA AND SENSATION.
§ III. INTENSITY AND QUALITY OF SENSATION. § IV. MEASURE-
MENT OF THE INTENSITY OF SENSATION.

§ I

SO soon as ever the dawn of knowledge had broken upon
us through the portals of the senses, we began to compare
objects, to reflect upon them. The first work of thought was to
-set things in their places, to transform the chaos of sense-
impressions into an intelligible cosmos. But after everything
•else has been arranged, there still remains something which has
as yet no place, — ourselves : our feeling, willing, and thinking ;
^o that the question arises : how can our own mental life be
made the subject of investigation like the objects of this external
world of things about us ? And yet — can such a question be
asked ? Is it not really self-contradictory ? It is as though we
required that the tone should hear itself, or the ray of light hi
sensed by itself.

It is, indeed, true that here, as we enter upon the study o\
.psychology, a peculiar difficulty presents itself. If we try to
observe our mental activities, the observer and the observed
•object are one and the same. But the most important condition
of a trustworthy observation is always thought to consist in the:
•mutual independence of object and observer. Nevertheless, we
should be overhasty if we disputed the possibility of psy-
chological observation in general because of this unavoidable
limitation of the science. Only so much is true : that the
peculiarities of the object, in this case as in others, imply special
conditions of its observation. These can be stated in two rules.
First : so long as we confine ourselves to introspection, without
•calling in any assistance from outside, mental processes may not
>be observed directly while they are taking place. We must

Analysis of Mental Processes- 13;

T

Ijmit- ourselves to analysing thenyso-Jar jisj3Q.ssihlftT from the
effects_jw.hich they leave hphind in our memory Secondly :
wherever in is possible, we must endeavour so to control our
mental processes by means of objective stimulation of the
external organs (particularly of the sense-organs, with the
physiological functioning of which definite psychoses are
regularly connected) that the disturbing influence which the
condition of observation tends to exercise upon them is
counteracted. This control is given by experiment. Not only
does experiment, here as elsewhere, enable us- to produce a
phenomenon, and to regulate its conditions,. at our pleasure: it
possesses in psychology an especial importance, in that it alone
renders self-observation possible during the course of a mental
process.

Let us now seek, in accordance with the first rule which we
established, to recall the general impression which any particular
mental experience has left upon us. This impression will always
be that of a composite process. Some parts- of it, images of
external objects, we designate Ideas ; others,, the pleasurable or
painful reactions of our own mind upon these ideas, Feelings ;
others, again, we term Efforts, or Impulses, or Volitions. It is
certainly true that these elements of mental life never occur
separately, but always in connection with, always in dependence
upon, one another. Nevertheless, it seems absolutely necessary,
at the beginning of a psychological investigation, to follow the
example of discrimination already set by language, and to
separate out the most important factors of this complex inner
life and subject each of them in turn. to. a special analysis.

Now, if these elements are all interconnected and inter-
dependent, it is clear that, other things equal, we might begin
the analysis which we contemplate with, any one of them.
Nevertheless, external reasons render it hardly possible to choose
any other method of procedure than that of commencing with
an investigation of ideas. We conceive of an. idea as the image
of some external object. We can, therefore, transfer to these
images of external objects the abstraction which we always
make in the case of the logical notions of the objects ; we
can consider them just as though the feelings, impulses, and
volitions, which in fact invariably accompany them, did not

14 Lectiires on Human and Animal Psychology
exist. On the other hand, in the case of these feeling's and

* o

impulses themselves, it is impossible to carry out an abstraction
of the kind, because we are not in a position even to describe
them without constant reference to the ideas with which they
are associated. Granted that this results merely from the fact
that all our designations took their origin from distinctions made
between objects of the external world, and were only applied
to our inner experiences at a comparatively late date, still
it remains true that this general trend of the development of
our knowledge necessarily determines the manner in which
psychology sets to work to analyse those inner experiences.

By an idea, then, we shall understand that mental state or
mental process which we refer to something outside of our-
selves, whether this attribute of externality be thought of as
directly applicable in the present, or as applied to an object
which has been directly given us in the past, or even as applied
to an object which is only possible, and not actual. Under
ideas, therefore, we include — (i) sense-perceptions, which
depend upon direct excitation of the organs of sense ; (2)
memories of such sense-perceptions; and (3) images of fancy, be
these what they may. The terminology adopted in many
Psychologies, according to which the images of memory and
fancy are alone designated ' ideas,' while the direct effects of
sense-impression are termed exclusively ' perceptions,' we must
judge to be unjustifiable and misleading. It lends colour to
the view that there is some essential psychological difference
between these two kinds of mental process, whereas such a
difference is nowhere discoverable. Even the reflection upon
which the distinction is based, — the thought that images of
memory and fancy do not correspond to objects actually pre-
sented to us, — is not universally valid. And, in the same way,
sense-perceptions may very well be themselves taken for
illusions of sense. So that the characteristics, by means of
which two kinds of ideas are distinguished, can never be more
than secondary, while the distinction itself cannot always be
satisfactorily carried through.

An idea, in the general sense in which we are here using the
word, is always something composite. A visual image is made
up of spatially distinguishable parts ; a sound is constituted of

Idea and Sensation 15

clangs, while it is also conceived of as coming to us in a certain
direction, — z.£., is associated with spatial ideas. Our first problem

et consists in the determination of

their simplest constituent elements, and in the investigation of
the psychological properties . jdfjjiese. We call the psycholo.-
gical elements of ideas Sensations. Thus we speak of the idea
of a house, of a table, of the sun or moon, but of the sensations
of blue, yellow, warm, cold, or of a tone of definite pitch. This
use of the word 'sensation/ we must notice, like the use of ' idea '
in the general sense mentioned above, has only become current
in recent psychology. In the earlier treatises, and still to some
extent in popular writings and belles lettres, we find the word
'sensation' employed with the same meaning as 'feeling.'
Here, and in what follows, we shall consistently adhere to the
definition just given, according to which sensations are merely
the simplest and most elemental psychological constituents of
the idea.

§ II

But the analysis of ideas into sensations does not conclude
the task which we have set ourselves, — the analysis of those
mental processes which are referable to external objects. For
in every sensation, again, we distinguish two properties, — one
which we name its strength or intensity, and another which we
call its quality. Neither can exist in the absence of the other.
Every sensation, be it of sound, heat, cold, taste, or what not,
is possessed at once of a certain intensity and a certain
quality. But, as a general rule, the two attributes can be
varied independently of each other. We can sound a musical
note, e.g., at first quite softly, and then, by gradually increasing
its strength, pass it through all possible degrees of intensity,
while its quality remains unaltered. Or we can strike different
notes one after the other, and so obtain different qualities,
while we still keep, if we will, one and the same intensity of
tone throughout. Here quality has changed ; intensity re-
mains constant. This possibility of varying the two consti-
tuents of sensation independently of each other depends upon
the fact that the motions in external nature, by the operation
of which upon our sense-organs sensation in general was origi-

1 6 Lectiires on Human and Animal Psychology

nally occasioned, present two aspects, either of which may also
vary without affection of the other.

The processes of motion which, by their operation upon our
senses, give rise to sensations, we commonly denominate
stimuli, or more particularly sense-stimuli. Accordingly, we
generally understand by stimulus the external motion-process,
which, after it has acted upon the sense-organ and been con-
ducted by sensory nerves to the brain, is accompanied by the
mental process of sensation. Thus we regard the sound-waves
of the air or the light-waves set up in surrounding space as
stimuli, corresponding to our sensations of sound and light. In/
the same way, those motion-processes which are aroused, by
the agency of such external stimuli, in our sense-organs and m
the brain, may also be regarded as processes of stimulation or
as constituents of the entire stimulation-process. For the sake
of clearness, we will call these last internal stimuli. If we seem
always to have the external stimuli primarily in mind when we
are speaking of the relation of ' stimulus ' to sensation, this is
only because they are the more easily accessible to objective
investigation. But wherever we can show good reason for the
belief that the peculiar form taken on by a stimulus-process in
the sense-organs, the sensory nerves, and the sense-centres of
the brain exercises a determining influence upon a particular
sensation, we shall, of course, be constrained to take into con-
sideration the character of the internal stimuli and the transfor-
mations which occur in the conversion of an external into an
internal stimulus.

Now, in whichever of these two senses we employ the notion
of ' stimulus,' we are able to vary both the intensity and the
form of any stimulation-process. But the intensity of stimulus
corresponds to the intensity of sensation, the form of stimulus
to its quality. (Thus, in the case of sound and light, the inten-
sity of the sensations corresponds to the extent or amplitude of
vibration, their quality to its rapidity. The quality of tone we
call pitch ; the quality of light, colour.) Although, therefore,
intensity and quality of sensation do not exist independently of
each other, yet psychological analysis is able to distinguish them
for its own purposes. In doing this, it is only completing an
abstraction which was begun when ideas were separated out

Intensity and Quality of Sensation 17

from the totality of mental life, and continued a step farther in
the subdivision of ideas into elementary sensations.

§ HI

We begin, then, with an investigation of the intensity of sen-
sations. And we leave for the present out of account everything
which has reference to their qualitative aspect.

If we compare with each other two different sensations of the
same modality, we are undoubtedly able to pass judgment re-
garding their intensities. Our judgment runs either : The sen-
sations are of equal intensity, or: They are not of equal in-
tensity. The midday sun we assert to be brighter than the
moon, the roar of a cannon louder than the crack of a pistol,
a hundredweight heavier than a pound. These comparative
judgments are taken directly from sensation. We really state
in them merely this : that the sensations which the sunshine,
the cannon, and the hundredweight arouse in us are more in-
tensive than the sensations which we have from the moon, a
pistol-shot, or a pound-weight. There is therefore possible a
quantitative comparison of sensations. We can say of two sen-
sations that they are of equal intensity, or that this one is of a
greater or less intensity than the other. There our measure-
ment of sensation ordinarily rests. We are not able to say how
much stronger or how much weaker one is than another. We
cannot estimate in the least whether the sun is a hundred or "a
thousand times brighter than the moon, the cannon a hundred
or a thousand times louder than the pistol. Our ordinary
measurement of sensation tells us only of ' equality,' of a ' more,'
or of a ' less,' never of a 'so much more ' or ' less.' And
this natural measurement is, therefore, as good as none at all
when an exact determination of intensity is required. Although,
perhaps, we may be able to observe that, as a general rule, in-
tensity of sensation increases and diminishes with intensity of
stimulus, yet we have not the remotest idea whether the two
vary in the same ratio, or whether one increases more slowly or
more quickly than the other. In a word, we know nothing of
the law of the dependence of sensation upon stimulus. If we
are to discover this, we must necessarily begin by finding a
more exact measurement for sensation. We must be able to

C

1 8 Lectures on Human and Animal Psychology

say : a stimulus of the intensity I occasions a sensation of the
intensity I, a stimulus of the intensity 2 a sensation of the
intensity 2 or 3 or 4, and so on. But, to do this, we must know
what it means to say that ' this sensation is twice,' or ' three
times,' or ' four times as great as that.'

Now, we have said above that it is possible to strike a note
first of all very gently, at an intensity at which it can only just
be heard, and then gradually to increase this intensity, until we
reach a point at which the note is as loud as it can be made.
Between these upper and lower limits the tone-sensation has
passed, not by leaps and bounds, but smoothly and uniformly,
through all its possible intensities. And the same is true of
other sense-impressions. From every sensation-quality we can
construct a one-dimensional series of sensation-intensities, which
pass over into one another without break or gap. In such a
series we may, first of all, quantitatively distinguish every mem-
ber from every other member ; we say that the one of two com-
pared sensations is the stronger, the other the weaker. But
more than that. We find no difficulty in stating, after succes-
sive comparisons, that the difference of intensity in one case
was greater than it was in another.

Now, as the result of these very obvious considerations, there
arise for psychological investigation two separate questions.
The first is : what is the basis of this natural measurement of
sensation-intensities, which enables us directly, without knowing
anything about the external affection of our senses, quantita-
tively to compare different sensations ? And the second, —
which, as soon as stated, becomes a problem in experimental
psychology, — runs : may not this crude and inaccurate natural
measurement be transformed into an exact one ; so that, e.g.,
we might be able to state how much stronger or weaker a given
sensation was than another with which we compared it ? We
will try to answer this second question first.

§IV

At first sight the attempt to measure the intensity of sensa-
tions may appear overbold. How can we hope to reach any
result when no definite measure is contained in the sensation
itself? But if we take a little time to consider how it is that

Measurement of the Intensity of Sensation 19

the measurement of magnitude in general is carried out, matters
will begin to look more hopeful.

For all measurement there is required a standard. And this
standard can never be the measured object itself. Thus we
may measure the time of an occurrence by a clock ; and what
the clock shows us is a uniform motion. Or we measure longer
periods of time by days, months, and years ; and these corre-
spond to uniformly repeated changes in external nature. That
is, we measure time by space. But to measure space, on the
other hand, we employ time. The length of the road over
which we have travelled we estimate by the time that the
journey has taken. And when we mark the successive divi-
sions upon a scale, we must do it in a time order. So that the
original measurement-units of space and time always coincide :
an hour is just as much an hour of space-experience as an hour
of time-experience. Space gives us our only means of measur-
ing time, and time our best means of measuring space. Never-
theless, there is a noteworthy difference in the way in which
each of these two measures depends upon the other. For
space-measurement it is only necessary that time should be al-
ready existent ; it is not requisite that we should possess an
exact measure of time. When we are constructing a scale, we
must mark in one unit after another ; but, that once done, we
do not need in every particular measurement to compute the
number of units which the scale embraces. We measure directly
with the whole scale ; that is, we take all at once, simultane-
ously, what was constructed gradually. To carry out the most
exact spatial measurement we need have no more than the
general notions ' earlier,' ' later/ ' simultaneous.' Then, when
space has been measured, we come back to time, in order to
divide it up by the help of our spatial measurements.

All exact measurement is, therefore, spatial measurement.
Times, forces, everything that can be considered as magnitude,
we measure by a spatial standard. Now, when we talk of com-
paring the intensities of sensations, we imply that sensations are
magnitudes. And although a direct comparison of sensation-
intensities does not enable us to do more than pronounce them
' less ' or ' greater ' or ' equal/ that is in itself no obstacle in
the way of obtaining an exact measurement. For at first we

2O Lectures on Human and Animal Psychology

possessed only the vague ideas of ' earlier,' ' later,' and ' simul-
taneous ' in the case of time ; and yet we are now able to
measure with very great accuracy temporal differences, the mere
cognition of which would have far transcended our original
powers. Indeed, it is just the same with sensation as with time,
and with all the other magnitudes which, like these two, are
primarily mental magnitudes. Temporal and spatial magnitudes
are alike distinguished in the first place only as ' equal,' ' greater,'
or ' less.' We quickly arrive at an exact determination of the
latter, since we are able to measure each new space-magnitude
by magnitudes already known. But the measurement of mental
magnitudes is apparently attended with greater difficulties. In
this sphere it was until recently only the movement of thought,
time, which had been subjected to an exact measurement, by
the substitution, for movement of ideas in us, of movements of
objects without us, and especially those movements with which
the impression of uniform regularity was invariably connected.

An exact means of measuring time cannot, then, be obtained
from time alone ; we must call in the aid of movement in space.
In the same way, we shall never be able to discover a means of
measuring sensation in sensation itself, but must take into con-
sideration the relation of its magnitude to other measurable
magnitudes. And there is no magnitude which presents itself \\
more obviously for this purpose than that of the stimulus, from
which the sensation arises. Indeed, the stimulus furnishes us
not merely with the most obvious, but with our only possible,
means of measuring sensation. There is no other magnitude
which stands in any such direct relation to the magnitude of
sensation.

The only assistance which sensation itself renders us in this
measurement is that of the ordinary distinction of sensation as
of ' greater,' Mess,' and 'equal' intensity. Everything else must
be derived from the measurement of stimulus. If two sensations
are of equal intensity, our first thought is that the external
stimuli are also of the same intensity in the two cases. But
measurement of them shows not seldom that this surmise is
wrong ; that stimuli of different intensity may occasion sensa-
tions of equal intensity. A weak eye finds ordinary daylight so
intense that it involuntarily closes ; but the normal eye displays

Measurement of the Intensity of Sensation 2 1

no such tendency, except when looking directly at the sun. If
we fall into a swoon, or into deep sleep, we do not sense the
prick of a needle which, in the waking state, would cause us
acute pain. Indeed, facts of that kind have been observed from
the beginning of time. This greater or less receptivity of the
organism, in face of external stimuli, we call sensibility or excita-
bility. We say that a weak eye is more excitable than a strong
one ; that we are more sensitive awake than asleep. But we do
not ordinarily think of measuring this excitability. And yet the
measure is given at once, if we only ascertain the intensities of
the stimuli which, on different occasions, give rise to a sensation
of equal intensity. If the stimuli are of equal intensity in both
cases, the excitability is the same ; if the stimulus in the first
case were twice or three times as strong as it is in the second, the
excitability in the former experiment was half or a third as great
as it is in the latter. In short, excitability is inversely propor-
tional to the intensity of the stimuli employed for the production
of equally intensive sensations.

Already, then, we have gained one result, which is not un-
important for our proposed measurement. We have discovered
a method of eliminating the differences of excitability which
may be found to exist in different individuals or in the same
individual at different times. And we are thereby in a condition
to propose and define a unit of excitability, such as has been
universally accepted for time, — supposing, of course, that its
proposition shall prove to possess any real significance.

A further basis of measurement is given with the increase and
decrease of sensation-intensity. What we all know with regard
to this is only that the intensity of sensation increases and de-
creases with the intensity of stimulus. If the ' sound in our
ear ' increases, we know that the external sound has become
louder, always provided that we have no reason to assume a
change of sensibility in our sense-organs. Originally this con-
clusion regarding increase of the external stimulus was merely
an inference from increased intensity of sensation. Not until
we have made those physical processes which constitute the
stimulus the object of separate investigation can we attain to
the definite conviction that this conclusion was correct. But in
pursuing such an investigation we come to make stimulus inde-

22 Lectiires on Human and Animal Psychology

pendent of sensation, and so are on the road towards the dis-
covery of a valid measurement of stimulus.

Now, if our entire knowledge were confined to this fact, that
sensation increases and decreases with stimulus, we should not
have gained very much. But there are facts of direct and un-
assisted observation which tell us something, even if in the most
general terms, of the law which governs the intensive relations
of stimulus and sensation.

Every one knows that in the stillness of night we hear things
which are unperceived in the noise of day. The gentle ticking
of the clock, the distant bustle of the streets, the creaking of the
chairs in the room, impress themselves upon our ear. And
every one knows that amid the confused hubbub of the market-
place, or the roar of a railway-train, we may lose what our
neighbour is saying to us, or even fail to hear our own voice.
The stars which shine so brightly at night are invisible by day ;
and although we can see the moon in the day-time, she is far
paler than at night. Every one who has had to do with weights
knows that if to a gramme in the hand we add a second gramme,
the difference is clearly noticed ; but if we add it to a kilo-
gramme, there is no knowledge of the increase.

All these experiences are so common that we think them
self-evident. Really, that is by no means the case. There
cannot be the least doubt that the clock ticks just as loudly by
day as by night. In the clamour of the street or amid the
noise of the railway we speak, if anything, more loudly than is
usual. Moon and stars do not vary in the intensity of their
light. And no one will deny that a gramme weighs the same
whether it is added to one gramme or to a thousand.

The sound of the clock, the light of the stars, the pressure of
the gramme weight, — all these are sensation-stimuli, and stimuli
whose intensity always remains the same. What, then, do
these experiences teach us ? Evidently nothing else than this :
that one and the same stimulus will be sensed as stronger or
weaker, or not sensed at all, according to the circumstances
under which it operates. But what kinds of change in the cir-
cumstances are there, which can produce this alteration in sen-
sation ? On considering the matter closely, we discover that
the change is everywhere of one kind. The tick of the clock is

Measurement of the Intensity of Sensation 23

a weak stimulus for our auditory nerves, which we hear plainly
when it is given by itself, but not when it is added to a strong
stimulus of rattling wheels and all the other turmoil. The
light of the stars is a stimulus for the eye ; but if its stimulation
is added to the strong stimulus of daylight, we do not notice it,
although we sense it clearly when it is joined to the weak
stimulus of twilight. The gramme weight is a stimulus for our
skin which we sense when it is united to a present stimulus of
equal strength, but which vanishes when it is combined with a
stimulus of a thousand times its own intensity.

We can, therefore, lay it down as a general rule that a stimu-
lus, in order to be noticed, may be so much the smaller if the
stimulus already present is weak, but must be so much the
larger the stronger this pre-existing stimulation is. From this
alone we can see, in a general way, how our apprehension of a
stimulus depends upon the intensity of it. It is plain that this
dependence is not quite so simple as might have been expected
beforehand. The simplest relation would evidently be that we
should estimate increase of sensation in direct proportion to
increase of stimulus-intensity. So that if the sensation I should
correspond to a stimulus of the intensity I, sensation 2 would
correspond to intensity 2, and sensation 3 to intensity 3, and
so on. But if this simplest of all relations prevailed, a stimu-
lus added to a present strong stimulus would occasion as great
an increase in sensation as if it were added to a present weak
stimulus ; the light of the stars would make as large an addition
to the daylight as to the night. This we know not to be the
case ; the stars are invisible by day. The increase which they
occasion in our sensation is not noticeable, whereas this increase
is very considerable indeed in the twilight. . So that this much
is made out as regards our comparative measurement of sensa-
tion-intensities, that they do not increase proportionally to the
increase of stimulus, but more slowly. But when we attempt
to decide what the relation which obtains actually is, everyday
experiences do not suffice. We have need of exact and special
measurements.

However, before we apply ourselves to the task of making
these measurements, it is necessary that we should be quite
clear as to the meaning of the questions which are before us

24 Lectures on Human and Animal Psychology

and the importance of the answers which we may expect to find
to them. If we increase two stimuli of different intensities, —
e.g., a gramme and a kilogramme,- — by the same unit, — e.g., by
the pressure of a gramme, — we come upon the fact that the ad-
dition to the smaller weight is quite plainly perceived, whereas
the addition to the larger one is almost or altogether imper-
ceptible. This fact may be interpreted a priori in two ways,
(i) It may be that the addition made to the stronger stimulus
produces absolutely a smaller increase in sensation than the
same addition made to the weaker. (2) Or it may be that the
sensation-increase is the same in both cases, but that the
stronger stimulus requires a greater increase in sensation than
the weaker, if the differences are to be equally clear in conscious-
ness. If the first hypothesis is correct, the measurements which
we are to make will have direct reference to the relation be-
tween stimulus-increase and the corresponding sensation-in-
crease ; if the second, then the law of which we are in search
will refer only to our apprehension and comparative estimation
of sensations, and not to these themselves. Now, without these
activities of apprehension and comparison, it is impossible for
us to formulate any judgment whatsoever concerning sensation-
intensities, from which it follows that the results of our measure-
ment of sensation must, in the first instance, be interpreted on
the alternative hypothesis : that all that we can get at directly
is the relation between alteration of stimulus and our appre-
hension of this alteration. It was with this in mind that I was
careful to say above, not that a given stimulus-increase produces
a smaller sensation-increase when added to a strong, than when
added to a weak, stimulus, but that in our estimation this in-
crease is smaller. If the absolute sensation-increase is smaller,
that can only be due to the working of another law, — that of
the parallelism of our estimation of a sensation-increase and its
actual magnitude. Now, obviously, an answer to the question
of the validity of such a hypothesis as that can only be looked
for at the conclusion of a detailed investigation of the relation
existing between the intensities of stimulus and sensation. This
is the investigation upon which we are now to embark. You
will, perhaps, allow me, for the sake of brevity, to speak in what
follows simply of ' sensation,' when I should more correctly say

Measurement of the Intensity of Sensation 25

" apprehension ' or ' estimation of sensation.' But I shall do
so with the repeated caution that this mode of expression is
only provisional, and with the assurance that I shall not fail in
a later lecture to enter fully upon the question whether the im-
plicit assumption that our apprehension of alterations in sensa-
tion-intensity runs parallel with the alterations themselves is
correct, or whether it must ultimately give place to some other.

This being understood, then, the problem immediately before
us takes the following shape. We are to determine what in-
crease of sensation corresponds to equal increases of stimulus,
or, in other words, to discover what stimulus-increase corre-
sponds to equal increases in sensation.

How to execute these measurements is something which our
•everyday experiences suggest. A direct measurement of sensa-
tion-intensities we saw to be impossible. It is only sensation-
differences which we can take account of. Experience showed
us what very unequal sensation-differences might correspond to
equal differences of stimulus. In most cases we find that the
same stimulus-difference would be sensed or not sensed accord-
ing to circumstances ; that, e.g., a gramme is sensed when added
to another gramme, but not when added to a kilogramme. We
should think very much less of the statement that a gramme
added to a gramme produced a considerable difference, added
to a kilogramme a slight difference, in sensation. And the
reason is not far to seek. It is difficult to say whether one
sensation-difference is just smaller or just larger than another ;
but we have generally no hesitation in calling two sensations
equal. We are quite sure that the stars are invisible by day ;
but we might be in doubt as to whether the full moon is brighter
by night than in the day-time. Our inquiry will, therefore, lead
to results most quickly, if we start out with some arbitrary
stimulus-intensity, observe what sensation it arouses, and then
see how long we can increase the stimulus without having the
sensation seem to change. If we carry out such observations
with stimuli of varying magnitude, we shall certainly be obliged
to vary the stimulus-increase which is just capable of producing
a difference in sensation. A light, to be just visible in the twi-
light, need not be nearly so bright as starlight ; it must be far
brighter to be just perceptible by day. If now we institute

26 Lectures on H^lman and Animal Psychology

these observations for all possible stimulus-intensities, and note
for each intensity the magnitude of the stimulus-increase neces-
sary to produce a just perceptible increase of sensation, we shall
get a series of numerical values, in which is definitely and im-
mediately expressed the law according to which sensation alters
as stimulus is increased.

Experiments by this method are especially easy to carry out
upon the sensations of light, sound, and pressure. We will con-
sider the last of these first, since they are the most simple. The
experimenter lays his hand comfortably upon a table. The
chosen weight is placed upon it. Then a very small weight is
added to this, and the question put whether the observer, who,
of course, must not look at his hand during the experiment,
notices any difference. If the answer is negative, a somewhat
larger weight is taken, and the same procedure is continued
until the increment of weight is found, which is just large
enough to be sensed clearly. When an experiment has been
concluded with one standard weight, a second and third are
taken, and so on, until the magnitude of the just necessary in-
crement of weight has been determined for a sufficient number
of standards.

We find a surprisingly simple result. The addition to the
original weight, which is just enough to produce a noticeable
difference in sensation, always stands in the same proportion to
it. Suppose, e.g., that we had found that the necessary addition
to a gramme was a quarter of a gramme. Then if, instead of
grammes, we took pennyweights or ounces or pounds, we should
have to add a quarter of a pennyweight to the pennyweight, a
quarter of an ounce to the ounce, a quarter of a pound to the
pound, in order to obtain a just noticeable difference. Or, if
we confine ourselves to grammes, we must add two and a half
to ten, twenty-five to a hundred, two hundred and fifty to a
kilogramme.

These figures explain the familiar fact that the difference be-
tween heavy weights, to be cognisable, must be larger than the
difference between light ones. But they also give us the exact
formulation of the law which governs the relation of sensation
of pressure to force of pressure exerted. You can hold this law
in mind by remembering a single number, the number ex-

Measurement of the Intensity of Sensation 27

pressing the proportion of the added weight to the standard.
Experimental results show that this proportion is, on the
average and approximately, that of 1:3. Whatever magnitude
of pressure may be exerted upon the skin, we sense its increase
or decrease so soon as the amount added to or subtracted from
it is one-third of the original.

Experiments of the same kind, but in greater number and
with greater accuracy, have been made with lifted weights.
Here, of course, the conditions are not so simple. When we
lift a weight, we have not only a pressure-sensation in the hand
which holds it, but also a sensation in the muscles of the arm
which raise hand and weight together. This second sensibility
is much finer than that of pressure proper. Indeed, it has been
experimentally shown that if lifting is allowed, an addition of
merely y-^ to the original weight produces a difference in sensa-
tion. Our sensibility to weight with lifting is, therefore, some
five times as great as our sensibility to weight which simply
exerts pressure. And the law of the dependence of sensation
upon stimulus may be similarly expressed in terms of the sensa-
tion of lifting, the fraction ^ being replaced by y^- or -j^. This
proportion holds whether the weight is large or small, whether
we are speaking of ounces, pounds, or grammes. It tells us
that there must be added to a hundred grammes six, to a thou-
sand grammes sixty, to every standard weight j^j- of its own.
amount, if a difference in sensation is to be apprehended.

To determine the objective magnitude of weights , we employ
the balance ; to measure accurately the objective intensity of
light, we use a photometer, or light-measurer. This is in principle
an instrument by means of which the brightness of a given light
is measured by reference to, and
expressed in units of another light
of constant brightness. A very
simple form of the photometer is
that schematically outlined in
Fig. I. A vertical rod, s, is fixed
in front of a white screen, w. Be-
hind the rod is placed the light n,
the intensity of which is regarded
as the unit of measurement. Beside n is set the light /, whose

28 Lectures on Human and Animal Psychology

intensity is to be measured. Both lights throw a shadow on the
white screen. Neither shadow is as dark as it would be if there
were present simply the one light which produces it ; each is
illuminated by the other light, and the greater the intensity of
this other light, the brighter will the shadow appear. Suppose
that both shadows are equally bright ; that would mean that the
•intensities of the two lights are equal. But suppose, again, that
the shadow cast by the normal light, the brightness unit, is
darker than the other ; this means that the intensity of the light
which is to be measured is less than unity. We can readily
•determine how much less by moving the normal light somewhat
farther back, for it is a law of optics that the intensity of a light
is inversely proportional to the square of the distance of the
luminous body. If the light, which was standing at the distance
of one metre from the white screen, is moved in a straight line
to a distance of ten metres, the intensity of the light falling upon
the screen is reduced from 100 to I ; at the distance of ten
metres it is a hundred times less than it was at the distance of
•one metre. We can easily institute in this way a quantitative
•comparison of a light of unknown intensity with a given normal
light. We have only to shift the two lights to such distances
that the darkness of the shadows cast upon the screen appears to
:be precisely the same ; then we measure the distance of each
light from the screen, and the inverse ratio of the squares of
the two distances gives us the relation of the intensities of
the lights.

We can turn this same method to good account for the
measurement of the dependence of light-sensations upon inten-
sity of light-stimulus. The strong illumination of the shadowless
part of the screen and the weak illumination of the shadows both
give rise to light-sensations, which are of course the more
different the darker the shadows. If we set out with two lights
of equal intensities, situated at the same distance behind the rod
•(say, two exactly similar stearine candles), the two shadows will
'be of the same intensity ; i.e., they are equally different from the
bright background upon which they are thrown. If now we
move one candle farther and farther away, the shadow cast by it
becomes weaker, and its difference from the illuminated back-
ground less, till finally a point is reached at which this difference

Measurement of the Intensity of Sensation 29

vanishes altogether. By measuring first the distance of the
stationary candle from the screen, and secondly the distance of
the candle which has been moved so far back that its shadow
has just disappeared, we obtain the data necessary for the formu-
lation of the law of the increase of light-sensation with increasing
intensity of light-stimulus. So long as only the stationary
candle was there, the total illumination of the screen was due to
it. When the other candle is moved up from a distance its light
adds something to the whole amount of illumination present
But this increase is at first unnoticeable ; the point where it be-
comes noticeable is fixed by the appearance of a second shadow
of the rod. The place which this shadow comes to occupy is, of
course, illuminated by the nearer candle, and not by the more
distant one ; and as soon as the latter has approached near
enough to produce a noticeable increase in the total illumination
the shadow must appear ; it is an index, so to speak, pointing
to an increase of illumination. And we now possess, in the
inverse ratio of the squares of the distances of the two candles-
from the screen, the relation of those light-intensities which con-
dition a just noticeable difference of light-sensation. Suppose,.
e.g., that the first candle was placed at a distance of one metre,
and the second (which casts a just noticeable shadow) at a
distance of ten metres, then the light-intensities stand to one
another as 100 : I ; or, in other words, the intensity of the first
candle must be increased by one-hundredth, if its increase is to
effect an increase of sensation. We have here pursued exactly
the same method as in our experiments with weights. There we
added to a heavy weight a lighter one, which just noticeably
increased the sensation of pressure ; here we add to a strong
illumination a weaker one, which just noticeably increases the
light-sensation. It only remains to extend these observations to
different stimulus-intensities, as was done in the experiments
with weights. Just as we varied our normal weights, so must we
vary the luminosity of the standard candle by known amounts.
That is very easily done. It is only necessary to move the
candle backwards or forwards, and to calculate its luminosity
from the distance at which it stands from the illuminated screen.
Experiments made in this way soon convince us that the dis-
tances of the two candles always bear the same relation to one

30 Lectures on Human and Animal Psychology

another. If the second candle had to be placed at a distance of
ten metres when the first stood at one metre, it must be placed
at a distance of ten feet when the latter stands at one foot, at
twenty metres or twenty feet when the distance in the other
case is two metres or two feet, from which it follows that light-
intensities which condition a just noticeable difference of sensa-
tion always preserve the same relation to one another. They
stand to each other as I : 100, as 2 : 200, etc. But this is the law
which we discovered in our experiments with weights, and the
law can just as well here be expressed by the number defining
the relation of the just noticeable increase of illumination to the
original illumination. This number is approximately y^- ; that
is, every light-stimulus must be increased by Y^-, if its increase
is to be sensed.

It is not hard to institute similar experiments in the sphere
of sound. The intensity of the sound produced by the fall of a
body upon some underlying surface increases with the magni-
tude of its weight and the height of its fall. If we always em-
ploy the same body, we can vary the intensity of the sound at
will by varying the height of fall. Intensity and height of fall
are directly proportional to one another. A fall from twice or
three times the standard height produces a sound twice or three
times as loud as the normal sound. A good way of turning
this principle to account for the investigation of sound-intensi-
ties which do not differ very greatly from one another is indi-
cated in the schematic representation of the sound-pendulum

given in Fig. 2. We take
two ivory balls, / and q, of
exactly the same size, and
suspended by cords of equal
length. Between the balls is
placed a block of hard wood,
c. If one of the two balls is
let fall from any chosen height
against the block, the result-
ing sound is directly propor-
tional to the height of its fall,

which can be measured by the angle through which the ball
was raised from the position of rest. The angle is read off from

'IG'2'

Measurement of the Intensity of Sensation 3 1

a graduated circular scale placed behind the block. The height
of fall of the ball p, e.g., is the distance ac ; for the ball q} the
distance be. That is, the balls strike the block with the velocity
which they would have possessed had they fallen vertically from
the points a and b. If ac and be are made equal by moving both
balls through the same angle, the two sounds are naturally of
equal intensity ; but if they are different, the sounds are also of
different loudnesses. As we pass by slow degrees from equality
to larger and larger differences of height of fall, dropping the
balls in quick succession, so that the sounds may be accurately
compared, we find that for some time there is no noticeable
difference of sound, despite the difference in height of fall. Not
until this difference has reached a certain magnitude does the
difference of sound begin to be noticeable. At that point the
height of fall is measured for both balls. The difference, of
course, gives us the amount by which a standard sound-intensity,
measured by the total height of fall, must be increased if we are
to obtain a just noticeable difference of sensation. Suppose, e.g.,
that the first ball had fallen through ten centimetres and the
second through eleven. That would mean that the standard
sound-intensity must be increased by -^ before a difference
could be sensed. By making similar measurements over a very
large number of heights of fall, we shall learn whether this
relation is constant when the sound-intensity is increased or
diminished. Just the same is found to hold here as in the case
of weights and light-intensities : the relation of stimulus-incre-
ment to stimulus-intensity always remains the same. Every
sound must be increased by about one-third for the production
of a clear increase of sensation.

We have found, then, that all the senses, whose stimuli we
can subject to exact measurement, obey a uniform law. How-
ever unequal may be the delicacy of their apprehension of sen-
sation-differences, this law is valid for all : that the increase of
stimulus necessary to produce an equally noticeable difference
of sensation bears a constant ratio to the total stimulus-inten-
sity. The figures which express this ratio in the several sense
departments may be shown in tabular form as follows : —

32 Lectures on Human and Animal Psychology

Light-sensation . . . y^-

Muscle „ . . . tV

Pressure „ ( ±

Sound „ )

These figures are far from giving as exact a measure as might
be desired. But they are at least adapted to convey a general
notion of the relative sensibility of the different senses. First
of all stands the eye. Next comes muscle ; the muscular sen-
sation affords an accurate measure of the differences of lifted
weights. Last, and on an approximate equality, stand the ear
and the skin.

This important law, which gives in so simple a form the rela-
tion of our apprehension of sensation to the stimulus which
occasions it, was discovered by the physiologist Ernst Heinricb
Weber, and has been called after him Weber's law. He, how-
ever, examined its validity only in special cases. That the law
holds for all departments of sense was proved by Gustav Theodor
Fechner. Psychology owes to him the first comprehensive in-
vestigation of sense, the foundation of an exact theory of sen-
sation.

LECTURE III

§ I. ESTIMATION OF THE INTENSITY OF SENSATION. §11. MATHEMATICAL
EXPRESSION OF THE LAW OF SENSATION-INTENSITIES. § III. SIGNI-
FICANCE OF NEGATIVE SENSATION-VALUES ; UNIT OF STIMULUS AND
UNIT OF SENSATION.

§1

THE question might, with some show of reason, be raised
as to whether the law which we have discovered is valid
for our quantitative estimation of sensation-magnitudes in general,
or whether it possesses only a more limited importance. For
all that we have directly ascertained is this : in what proportion
the just noticeable sensation-difference stands to the stimulus-
increment which conditions it. But, as a matter of fact, it will
be easily seen that the determination of this proportion is simply
a special case in the determination of a more general relation
of dependency.

No one will doubt that it is possible to pass gradually by
very small sensation-differences to very large ones. Suppose
that we take a sensation which has increased by a just notice-
able magnitude, and that we allow this second sensation to
increase again by a just noticeable difference ; the difference
between the first and third will be clearer than that between
the first and the second. And if we proceed in this way, always
increasing by a just noticeable increment, we shall finally arrive
at a sensation-intensity which is very much greater indeed than
that of the sensation from which we set out. And we shall
have correspondingly reached a very considerable difference of
stimulus-intensity. Had we passed directly from the weak
stimulus to the strong, and therefore from the weak to the
strong sensation, we should never have been able to gain any
exact information as to the dependency of sensation upon
stimulus. Taking steps of such length from sensation to sensa-
tion, we should not have been able to decide whether the

33 D

34 Lectures on Human and Animal Psychology

sensation had increased in the same proportion as the stimulus.
A result which we could only have attained to with difficulty,
if we had tried to alternate between large sensation-differences,
comes out of itself if we gradually increase the stimuli in such
a way as to pass invariably from one just noticeable sensation-
difference to another. By how much any one sensation exceeds
any other is just as difficult to determine from their immediate
comparison as it would be to say how many more grains of
wheat there are in one heap than in a second. If we want to
know that, we must just set to work and count every single
grain. And, similarly, if we wish to learn how much more
intense a second sensation is than a first, our best method will
be to analyse the sensations into those elements which are the
equivalents of just noticeable differences.

It is true that in following this method we can never compare
more than one sensation with another. But if we have once
established a sensation-unit, we can easily determine by com-
parison with it the magnitude of any other sensation whatever.
Let us assume that we have adopted, as the unit of cutaneous
pressure-sensibility, the sensation occasioned by the pressure of
I gramme. We have found that the relation in which sensa-
tion increases with increase of stimulus is expressed in the case
of pressure-sensations by the fraction ^ ; i.e., the external
pressure must increase by ^ of its intensity, if it is to produce
a just noticeable increase of the pressure-sensation. We can,
therefore, just distinguish i-^- grammes from I gramme ; while
we can only distinguish 2\ from 2, or 3|, — i.e., 4 grammes
from 3, etc. Now if we regard all equally noticeable sensation-
increments as equal magnitudes, then obviously the magnitude
of the just noticeable sensation-increase occasioned by the
pressure of I gramme is equal to the just noticeable increase
of the sensation occasioned, e.g., by a pressure of 10 grammes.
So that we may think of any increase of a sensation of whatever
intensity as being entirely made up of a number more or less
of just noticeable sensation-increments. We may assume that
these begin at the point where the external stimulus just suffices
to excite a sensation. Now, then, we are in a position to give
quantitative expression to sensation-intensity, however great or
small this may be. One sensation is twice, three times, or four

Estimation of the Intensity of Sensation 35

times as intensive as another, when it is made up of twice, three
times or four times as great a number of equal sensation-in-
crements. This system of measurement presupposes that we
follow up sensation in its gradual increase. But that is the
case, strictly speaking, in all measurement. All the measures
which we possess consist of a series of measurement-units.
The unit which we have chosen for sensation is the just notice-
able increment. If a sensation is made up of four times as
many units as another, then it is four times as great as that
other ; just as a scale on which four inches are marked is four
times as long as one which measures only one inch. If we
merely estimated the relation of the two scales as regards length,
our comparison would perhaps not be very accurate. An exact
judgment is only possible by the application to each of the
same measurement-unit. And it is precisely similar with sensa-
tion.

The method of measuring sensations of various intensities by
the addition of just noticeable differences would, however, be
very cumbrous. We can plainly reach our end very much
more quickly so soon as we have learned the law according to
which sensation-increase is correlated with increase of stimulus.
Having formulated such a law, we could predict that exactly
so great an increase of stimulus would condition so great an
increase of sensation.

As a matter of fact, we possess a law of this kind. Weber's
law tells us that a stimulus must always increase in a like ratio,
if the corresponding increase of sensation is to be equally
noticeable. So that, for practical purposes, any question of
sensation-measurement may now be put in the form : by how
many units, or by how many equally noticeable magnitudes
will, on Weber's law, a given sensation be increased, if we
increase the stimulus by a definite number of its units ? Or
conversely : how great must a given stimulus be made, in order
that the sensation may increase by a definite number of sensa-
tion units ? Let us take pressure-sensations once more, for
purposes of illustration. You will remember that the sensation
occasioned by I gramme must be intensified by -£ gramme for
it to increase by I unit. Suppose now that we wished to learn
how much the pressure must be intensified for the sensation to

36 Lectures on Human and Animal Psychology

FIG. 3.

increase by 6 such units. We imagine
the sensation-units arranged upon a scale.
At the zero-point of this scale, which we
will place for the moment arbitrarily at a
stimulus of I gramme, we draw a perpendi-
cular of any length to represent the gramme.
In order now to represent the magnitude of
pressure for a sensation increased by I unit,
we must lengthen the perpendicular at I
by •£ of the perpendicular at o.

Similarly at 2, we must lengthen the perpendicular I by •£ ;
at 3, the perpendicular 2 by ^, etc. Since the perpendiculars
constantly increase, these incremental parts will also of course
become larger ; we have to draw upon our scale lines of con-
tinually increasing length. And it is plain that the magnitude
of each of these lines stands to that of the perpendicular drawn
at zero in the same relation in which the weight, occasioning
the sensation-increase marked upon the scale, stands to the
initial weight of one gramme. The question being, what weight
has to be applied to produce a sensation-difference equal to 6
sensation-units, we have only now to measure how much longer
the perpendicular at 6 is than the perpendicular at o.

If we connect the upper ends of the perpendiculars drawn
upon our sensation-scale to represent stimulus-magnitudes, we
obtain a curved line ascending more steeply as we approach the
higher values of the scale. This curve obviously shows the de-
pendence of our measurement of sensation-intensities upon the
corresponding stimuli, not only for the points I, 2, 3, etc., but
also for all points situated between these, e.g., for 15, i \. If we
wish to discover what intensity of stimulus corresponds to some
particular point lying between two unit values, we need only
connect the point in question by a perpendicular with the curve
representing the alteration of stimulus. The magnitude of the
required stimulus is represented by the length of this perpen-
dicular. The sensation-difference which corresponds to a point
on the scale lying in this way between two unit values is, of
course, not perceptible by us ; but it would be quite wrong to
infer from this that it has no existence whatsoever. For we can
only reach perceptible differences by heaping up, as it were, a

Estimation of the Intensity of Sensation 37

great number of imperceptible differences. It is mere chance
that the just noticeable sensation-differences in our illustration
fall exactly at the points I, 2, 3. If we were to take as our
initial weight £ or f gramme instead of I gramme, the whole
scale would be shifted to the left, and the points where the
numerals now stand would then fall between two numerals of
this second scale. But the law of the variation of sensation-
with stimulus-intensity would remain precisely as before. Our
measurement on any scale is discrete, but the scale itself is con-
tinuous. We cannot, you see, proceed from one weight to
another so as to pass through all possible intermediate weights ;
but we interpolate between 2 grammes ^ T^, 10*00> or perhaps
even a 6 ^ 0 0- of a gramme, if we wish to be exceedingly accurate
in weighing. But no one would maintain that a weight of less
than 10ooo of a gramme is no weight at all. And just as there
are differences of weight, which no balances can detect, so there
are differences of sensation, which we are unable to cognise.

Now there can be no doubt that the scale which we have been
using to measure sensations, is not one particularly suited to its
purpose. We started out from the simplest possible stimulus-
magnitude, from the pressure of I gramme, our unit of weight.
We made the zero-point of our scale correspond to this point,
and proceeded to fill in our sensation-units to the right of it.
But when we have done this, we have not put ourselves in a
position to determine anything more than by how much we must
increase the weight of a gramme in order to obtain a definite
increase of sensation-units ; or how many sensation-units have
been added to the pressure sensation of one gramme, when we
are being stimulated by a weight of definitely greater magni-
tude. We do not know in the least how great the sensation is
which is occasioned by I gramme ; i.e., how many sensation-
units are to be reckoned to the left of the zero point on one
scale. The way to determine this is obviously to set out, not
from a definite stimulus-unit, but from the unit of sensation ;
and to measure onwards in terms of this, from the point where
sensation begins. If, then, we wish our scale to be a natural one,
we shall take the point at which sensation begins for our zero-
point. But this is not at the same time the zero-point of
stimulus. Some stimuli are so weak that they are not sensed at

38 Lectitres on Human and Animal Psychology

all. In order to occasion a sensation, the stimulus must have
attained a definite magnitude, which in each case is determined
by the character of the sense organ. The case here is similar
to that of sensation-differences. These are only perceived if
the stimulus-differences are of a certain intensity. In the same
way sensations in general are only perceived when the stimulus
has attained a certain magnitude. It might, perhaps, be sup-
posed that the two cases are not only similar, but identical •
that the intensity of the stimulus necessary to produce a sensa-
tion at all is equal to the intensity of stimulus-difference which
gives rise to a just noticeable difference of sensation. But it
may be easily seen that this is impossible. The intensity of a
stimulus-difference is always directly dependent on the total
stimulus-intensity, and decreases with decrease of the latter. So
that if the stimulus becomes infinitely small, we should be forced
to assume that the stimulus-difference must also become infinite-
ly small. That however is contradicted by experience, which
shows us that every stimulus must have attained a definite
measurable magnitude, if it is to produce a sensation.

If, therefore, we follow our former method, and erect per-
pendiculars to express the stimuli which correspond to the
series of sensations, we must draw at the zero-point a line whose
length represents the magnitude of the stimulus which occasions
a just noticeable sensation. If we keep to our sensations of
pressure, and find that -^ of a gramme is the magnitude of
weight sufficient to excite a just noticeable pressure-sensation,,
we shall represent this weight by a perpendicular at the zero
point. At i, which is removed from o by a just noticeable differ-
ence, the vertical representing the stimulus will, in accordance
with the dependency of sensation upon stimulus, be -^ longer ;
i.e., the stimulus whose original magnitude was -£$ or yf^ will
here be yj^-, etc. In short, we obtain the same relative increase
of stimulus and sensation that we had upon our former scale
(Fig. 3), the only difference being, that the new vertical at O
now stands for -^ of a gramme, and not for I gramme.

To answer all the questions that come up in any sense-depart-
ment, then, two measurements are in general sufficient ; first, the
measurement of the constant relation in which sensation-intensity
varies with variations in the intensity of the stimulus ; and

The Law of Sensation-intensities 39

secondly, the measurement of the just noticeable sensation.
The first measurement enables us to divide up the sensation-
scale ; by calling in the aid of stimuli we can mark it off into
equal parts. The second measurement gives us its zero-point,
and thus renders the scale ready for practical use. If we have
found in the sphere of pressure-sensations that the constant ratio
is ^, and that the just noticeable sensation is produced by -^
gramme, we can dispense with all further measurement, and
solve any problem presented to us. Suppose that we wish to
know the intensity of a sensation excited by the pressure of I
gramme. We take our scale, and begin with the zero-point.
The pressure at o is -^ gramme ; the pressure at I is ^ greater ;
the pressure at 2 is •£ greater than it was at I, etc. We proceed
in this way till we come to a pressure of I gramme, and then
count up how many units of our sensation scale have been em-
ployed up to that point. We shall find that we have used nearly
14 units ; so that if we press upon the skin first with •£$, and
then with I gramme, we have passed over 14 just noticeable
differences. And the nearer we come to I gramme, the greater
are the pressure-differences to which the just noticeable differ-
ences correspond. The first unit corresponds to £ of the original
stimulus, or -j^- gramme. If the sensation increased directly as
the stimulus, our 14 units would correspond to an increase of 4-|
or not quite £ gramme ; while, as a matter of fact, they require
an increase of pressure of •£$, or almost a whole gramme.

§ II

This method of determining the intensity of sensation by pro-
ceeding gradually from weak to strong stimuli through just
noticeable differences would, however, be exceedingly tedious
in practice. Direct observation would possess over it the advan-
tage of greater brevity. The question, therefore, suggests itself,
whether we cannot discover some shorter method, which would
permit us to pass at one step from -^ to I gramme, instead of
using, as we did above, no less than 14 intermediate stages.
This question may be answered in the affirmative, as a some-
what closer consideration of the dependency existing between
sensation and stimulus will convince us.

Sensations and stimuli are interdependent magnitudes. Both

4O Lectures on Human and Animal Psychology

are capable of numerical expression. The numerical values
which stand for sensations increase with the increase of the
numerical values of stimulus. The simplest relation in such a
case would plainly be this : that corresponding to the stimuli
expressible by the numbers I, 2, 3, etc., there existed sensations
which were also expressible by those numbers. We should then
say that sensation-intensity is directly proportional to intensity
of stimulus. This simple relation, however, does not hold ;
stimuli increase far more rapidly than sensations. Now there
are, of course, countless forms of the relations of dependency
existing between numerical values, where one numerical series
increases faster than the other. If, for instance, we multiply
every number by itself, we obtain from the series, I, 2, 3, 4
. . . another series, I, 4, 9, 16. . . . The first numbers
are known as the square roots of the second ; the latter are
called the squares, or second powers, of the first. So that if these
two series expressed the relation of stimulus and sensation, we
should say the sensation is equal to the square root of the
stimulus. A similar numerical series, differing from this only
by its more rapid increase, can be obtained by multiplying each
number by itself twice or three times, and so obtaining its third
or fourth power. If either of these series expressed the rate of
stimulus increase, we should say that the sensation is equal to
the third or fourth root of the stimulus. But sensation-intensity
increases neither as the square root, nor the cube root, nor as
any other root of the stimulus-intensity. This is plain from the
fact that the stimulus-increments which condition definite in-
creases of sensation-intensity stand in a constant ratio to the
total stimulus-magnitude. Since, therefore, the relative stimulus-
increments always remain equal, the relative numerical incre-
ments in the series of numbers representing the stimuli must
also be constant. This is not the case in the series cited. In
the series, I, 4, 9, 16 . . . e. g., the numerical increments
are successively 3, 5, 7, and the numbers to which these incre-
ments are referable, I, 4, 9 ; but the ratios -f-, -|, f-, are not equal.
If this case actually corresponded to the sensation-law, we must
have obtained the fractions, -f-, |-, ^, etc., or others which gave a
constant result when the division was made. But neither the
second nor the third nor any other powers give such a series.

The Law of Sensation-intensities 41

On the other hand, there is another numerical relation of very
general application which exactly corresponds to the relation
between stimulus and sensation.

If we cast a glance at an ordinary table of logarithms, we
notice that the numbers in it are entered in two columns ; one
contains the ordinary numbers, the other the logarithmic
numbers. We see at once that these latter increase more slowly
than do the ordinary numbers ; just as magnitudes of sensation
increase more slowly than magnitudes of stimulus. If the
number i, e.g., stands on the one side, we find o on the other, as
its logarithm. The logarithm of 10 is I, of 100 is 2, etc. Here
also, then, in the case of numbers and their logarithms, we have
two series which increase in very different ways. And if we
look more closely, we find that this similarity is more than
merely external. The logarithms of I, 10, 100, 1,000, are o, I,

2, 3. What is the relation of the increase of those numbers to
their magnitude ? When i is increased to 10, 9 is added ; when
10 is increased to 100, 90 ; when 100 to 1,000, 900. The ratios
of this increase are, therefore, -f-, -f-^, -f^-. But these ratios are
all equal, i.e., all equal to 9. Now this is an expression of the
law which regulates the increase of sensation. Sensations in-
crease by equal magnitudes, when the increase of stimuli is such
that each increment stands in a constant relation to the particular
total stimulus-magnitude ; and the logarithms increase by equal
magnitudes, when the increase of their numbers is such that
each increment stands always in the same ratio to the corre-
sponding numerical magnitude. So that we can say that sensa-
tions increase as logarithms when stimuli increase as their
numbers ; or, still more shortly — since we may express any
stimulus-magnitude by some definite number — sensation increases
as the logarithm of stimulus.

Logarithmic tables were naturally in use long before psycho-
logy felt the necessity of them. Indeed, the expression of the
dependency of sensation upon stimulus is merely that of a very
simple relation, of frequent occurrence in the expression of the
dependency of magnitudes in general. The logarithms o, 1,2,

3, e.g., differ each from its neighbour by the same amount, I ;
while the corresponding numbers I, 10, IOO, I,OOO, differ from
one another by the same multiple : i.e., by ten times their value

42 Lectures on Hitman and Animal Psychology

in each instance. But if this were the only rule we possessed
for finding logarithms, the process would be exceedingly tedious.
The matter is happily very much simpler. If we raise a number
to all its possible powers, we get from it, of course, other
numbers. Thus iol=io; io2=ioo; io3=i,ooo. It is clear
that by thus raising the powers of a single number we can
obtain any number whatsoever. For if we take the ij, i|-, i^
powers of 10, they give us numbers lying between 10 and 100 ;
the powers 2j, 2^-, 2\, give numbers between loo and 1,000.
And if we take all the possible fractional powers, we shall obtain
all the possible numbers between 10 and 100, between 100 and
1,000, etc. In order to obtain also the numbers which are
smaller than 10, we must not multiply the number 10, but
divide it so many times by itself. We must raise it, as the
mathematicians say, to negative powers. Thus io-1 — -j^; io-2
= -j-^j-, etc. But between io1 and io-1 stands 10° or io1-1 : i.e., I.
If we take as well the intermediate fractions of these negative
powers, there result all the possible fractional numbers ; while
between the powers o and I come all the numbers between I
and io. We have, therefore, obtained every possible number
simply by raising the single number io to all its powers. Now,
if we compare the powers o, I, 2, 3, with the corresponding
numbers I, io, IOO, 1,000, we see that the latter stand to one
another in the same ratio as the logarithms to their numbers.
The former increase by equal increments, when the numbers
resulting from the involution increase by equal multiples. The
indices of the powers are therefore nothing but the logarithms
of the numbers which we obtain by the process of involution.
And we can now formulate the sensation-law as follows : sensa-
tions stand to their stimuli as the indices to the numbers arising
from involution.

§ HI

But now a certain doubt may arise with regard to this
paralleling of indices and logarithms with sensations. There
are negative indices, as we have seen ; and, consequently>
negative logarithms. If we divide the number IO by itself once,
twice, three times, and four times, we obtain the powers
O, -i, -2, -3, or the logarithms o, -I, -2, -3. The number of these

Significance of Negative Sensation-values 43,

negative logarithms is just as unlimited as the number of the
positive. This will be perfectly intelligible when we remember
that the negative powers and logarithms signify fractions. If we
continue the series io-\ io-2, io-3, or ^ y^-, y^-V^ we reach
successively smaller and smaller fractions. Just as the series of
whole numbers only terminates at infinity, so with the series of
fractional numbers. If, then, we wish to reach zero by the
method which we have described, it will be necessary to divide
io by itself an infinite number of times. Thus the logarithm
corresponding to zero is negative, and infinitely large. But is
all this applicable to sensations ? Are sensations ever negative ?
And can there be sensations which, besides being negative, are
also infinite ?

When we speak of negative sensations, we ordinarily under-
stand by the term sensations which are opposite in direction to-
other sensations which we call positive. Cold, e.g.> is a negative
sensation as opposed to hot. But it would be equally correct
to call cold positive, and thus to make hot a negative sensation.
The terms v positive ' and ' negative ' are, here as elsewhere, the
expression of an opposition. The negative is by no means
nothing : it is just as much a real magnitude as the positive ;
and the terms we apply are in themselves arbitrary. A shop-
keeper reckoning up his effects, counts everything which he has in
the till, or that others owe him, as positive ; his own debts he
regards as negative. If, on the other hand, he is estimating his
debts, he considers them as positive, and the contents of the till,
and his loans as negative. The result is the same in both cases.
Or if a geometrician wishes to distinguish directions in space, he-
names that direction negative which he does not name positive ;
which becomes which is quite immaterial. Just in the same way
we characterise the logarithms of fractions as negative because
we have already used the positive denomination for the
logarithms of whole numbers. We must guard ourselves against
supposing that we have here anything more than a mere con-
vention, even though this convention is the most natural and
obvious.

The question arises then whether we may not speak of
negative sensations, using the word in the above sense of simple
opposition. No one will hesitate to answer this question in the

-44 Lectures on Human and Animal Psychology

affirmative, if it can be once shown that such an opposition
exists among sensations. It is of course unnecessary to say that
oppositions like that of hot and cold do not concern us in the
present instance. Hot and cold are differences of sensation-
quality, about the nature of which we have here as little
to inquire as about the differences between agreeable and
disagreeable, pleasant and unpleasant. It is true that these
attributes are predicated of sensations of opposite character.
And if we were subjecting these to a special investigation, we
might not only justifiably, but very naturally, express the
antitheses of hot and cold, pleasurable and painful, by positive
and negative magnitudes. But our business in this first instance
ns only with the intensity of sensation ; and all other sensation-
iproperties are, therefore, excluded* from our consideration.

We found the natural zero-point of our scale to be the point
where sensation begins, where we first sense at all. Can there
be sensations which are not sensed ; or does the putting of that
-question involve a contradiction of terms ?

There certainly is a contradiction. But it is only an apparent
-one, due to an equivocal use of the word ' sense.' We have
-already seen that there exist sensation-differences which are
not sensed (p. 22). It is obvious that two different meanings
have been given to the word. In its first signification the sensa-
tion is simply something which depends upon an alteration of
stimulus, no matter whether we detect this alteration or not.
But, secondly, it is our discovery of such alteration, which is
denoted by sensation. And this is equally true for sensations
'taken absolutely. In speaking of sensations which are
too weak to be sensed we are regarding them as something
independent of our apprehension of them ; we are considering
them merely as conditioned by external stimuli. We can put
the matter in this way. A sensation-difference is not at all
identical with a sensed difference ; the latter implies a definite
intensity of the former. And a sensation may exist long before
it can be sensed. We only sense it when it reaches a definite
intensity. But though in this statement we recognise the
equivocation, we have not done away with it. The equivocation
is explained by the fact that when the word first appeared in
•language the nai've consciousness which produced it knew only

Significance of Negative Sensation-values 45,

those sensations and sensation-differences which it was itself able
to recognise as such. Not till scientific reflection had arisen
was the human mind forced to the conclusion that there must
be sensations and sensation-differences- which it was inadequate
to recognise for the reason that sensations neither arise nor
alter abruptly, but only through continuous gradations.

So that there is nothing left for us but to use the word ' sensa-
tion ' here and in what follows to express all those sensations and
sensation-differences which we do- not perceive, but whose
existence we must assume to explain those which we do perceive,
as well as sensations in the narrower sense of processes which we
are able clearly to apprehend. Where it becomes necessary to
make a distinction we will call sensations and sensation-differ-
ences of the latter class ' noticeable/ and of the former ' unnotice-
able.' Now, since we observe that a sensation must have attained
a certain magnitude if it is to become noticeable, and that, other
things being equal, it gains in intensity the greater its magnitude
becomes, we are surely justified in- taking as the zero-point of
our sensation-scale the point where sensation becomes just
noticeable. That settled, we shall naturally call the noticeable
sensations, to the right of that point, positive; the unnoticeable
sensations, to the left of it, negative. For noticeable and
unnoticeable denote a direct antithesis, as valid as that of cold
and hot, or of opposing directions in space.

We conclude, therefore, that our comparison of the relation
in which sensation stands to stimulus with the relation of
logarithms to their numbers holds with regard to this further
point of the opposition between positive and negative. And
we can now produce our scale beyond the zero-point in a nega-
tive direction until the stimulus vanishes, as has been done in
Fig. 4. And now at length we have our sensation-law in its

most general form. How many
units must we enter on the
negative side to the left of o-
before we reach the zero-point
of the stimulus? The stimu-
lus zero-point in this connec-
tion is not, of course, the ex-
ternal process of movement

46 Lectitres on Human and Animal Psychology

affecting our sense-organs, and which has just attained the
lower limit of efficiency, but the internal stimulus in the brain
resulting from the former, and paralleled as physical process with
the mental process of sensation. For it may be assumed that
there are external stimuli too weak to reach the brain, whether
because of their inability to affect the organ of sense, or because
they cannot be conducted from it to the brain. This assumed,
where will the line which expresses the increase of stimulus
with increase of sensation cut the sensation-scale? We can
obviously extend our negative sensation-units to infinity with-
out arriving at that point ; for if we suppose, e.g., that the
stimulus decreases by ^ of its magnitude at each division of the
scale, it yet decreases more and more slowly ; and though at
last it becomes exceedingly small, it does not disappear so long
as the negative sensation-units which we are positing are ex-
pressible in numbers. Only when these numbers become
infinite may we assume that the corresponding stimulus-magni-
tudes are also infinitely small, i.e., so small that we may without
hesitation regard them as zero. Once more, then, we have the
same relation as that of logarithms to their numbers. If we
extend further and further the fractional series -fa, •^s, 10100, we
do not come upon any fraction, however small, which is not
greater than O. We should only reach o at infinity; and, there-
fore, the negative logarithm corresponding to it is infinitely
large. In the same way, we may conceive of a stimulus as
divided and subdivided as long as we please, and nevertheless
the smallest particle of it would still be a stimulus. The
stimulus only becomes equal to zero at infinity, and the nega-
tive sensation corresponding to a stimulus equal to zero must,
therefore, be infinitely great ; and since a negative sensation
means the same thing as an unnoticeable sensation, an in-
finitely great negative sensation will simply be that sensation
which is less noticeable than any other, just as it may be
asserted of o and oo that the first is smaller and the latter
larger than any other number.

Our analogy between the logarithmic law and the law of
sensation is now incomplete in one point only. We saw that
all possible numbers can be obtained by raising a single num-
ber to all its possible powers The positive powers give us the

Units of Stimulus and Sensation 47

whole numbers ; the negative, the fractions ; and the zero
power gives us unity. All these facts we have found to possess
a definite significance in the case of sensation. But we have
left one point still undetermined ; that is the number whose
involution gives us all the other numbers that are possible. In
the instance which we took, we raised the number 10 to the
powers o, I, 2, 3, and obtained the series I, 10, 100, 1,000. Had
we taken some other number than 10 and raised it to those
powers, we should have obtained a different series. It is im-
portant, therefore, to know what number it is which has been
chosen as the base by whose involution the other numbers are
expressed.

It is obvious that this must also be an important question for
the sensation-law, since sensations stand to stimuli as their in-
dices to the numbers obtained by involution ; and it is evident
that we can only say what stimulus-magnitudes correspond to
the sensations j, 2, 3, if we know what definite number was
taken as the base in this case of involution. Our choice of that
number is entirely arbitrary. For our sensation-scale it is im-
material ; it conditions only the divisions of the scale. We
shall plainly have the most convenient division if it is so carried
out that magnitudes of sensation may be calculated directly
from magnitudes of stimulus, and vice versd. But this is possible
only when sensation is the simple logarithm of stimulus, and
not some multiple or fraction of this logarithm ; and this
depends entirely on the absolute magnitude of our unit of
stimulus and our unit of sensation. Both of these magnitudes
may be arbitrarily chosen when we have once made it clear to our-
selves what they mean. We have already seen that the stimulus
must be taken as equal to I where the sensation is equal to o —
i.e., is just noticeable, for i°, 10°, 100°, are all equal to I ; or, in
other words, the logarithm of I is always o. That determines
once for all the magnitude of the stimulus-unit. Now, if the
sensation I is also to come at the point where its stimulus is the
number corresponding to the logarithm I, we must mark it (lO
being, e.g., the base employed) at the point where the stimulus
has attained the magnitude 10. Had 100 been the basal number,
we must have placed I where the stimulus had the magnitude
100, and so on. For iol=iO, IOO1— IOO, and every number

48 Lectures on Hitman and Animal Psychology

raised to the first power is equal to itself. Further, if we mark-
in more of our sensation-units, the divisions 2, 3, 4, take their
necessary places where the stimulus-magnitudes are 100, i,ooor
10,000, etc. For io2=ioo; io3= 1,000; io*= 10,000. This is
all required by our law, as we have seen, if the stimulus 10
corresponds to the sensation i ; so that now we have also de-
termined our sensation-unit. It is equal to the number which
we have chosen as base. Under these conditions, when the
stimulus is represented by the number obtained by involution,
the sensation corresponds to the index ; or the sensation is
equal to the logarithm of the stimulus.

In our ordinary logarithmic tables 10 is the base by whose
involution all the numbers are obtained. So that, if we wish to
calculate sensations from stimuli, we have only to call that
sensation I which is occasioned by a stimulus-magnitude ten
times as great as that which lies at the limit of noticeability.
Having done this, it is only necessary, when a particular
stimulus-intensity is given, to look up in the logarithmic tables
the number which expresses that intensity ; the logarithm in
the next column gives at once the magnitude of sensation. To
return to our previous example, — if a weight of -^ gramme pro-
duces a just noticeable sensation, we call -^ gramme stimulus
I. Pressure by ten times this stimulus, — i.e., by £ gramme, — we
call sensation I. Now it is easy to determine at what weight
the sensation is any whole or fractional number of times
greater, or by how much the weight must be increased in order
to condition a particular increase of sensation. If we wish to
get a sensation 2.\ times as intense as sensation I, we refer to
our table, and find for the logarithm 2'5 the number 316. That
means 316 stimulus-units, or V?r6=6'3 grammes. Or if the
problem is to determine how great the sensation is which is
occasioned by a stimulus of 5,000 units (100 grammes), we look
up the number 5,000, and find its logarithm, 3*698. That is, a
pressure of 100 grammes produces a sensation which is 3-698
times as great in intensity as the sensation arising from the
pressure of ^ of a gramme.

We have now completely answered the question which was
before us. Not only have we discovered the law of the de-
pendency of sensation upon stimulus, but we have indicated

Significance of Negative Sensation-values 49

the method by which the intensity either of sensation or of
stimulus can be calculated when the intensity of its correlate is
given. This method is simplicity itself, for it presupposes no
more knowledge than that of the multiplication-table and no
more apparatus than a book of logarithms.

LECTURE IV

§ I. THE JUST NOTICEABLE SENSATION. §11. UPPER AND LOWER LIMIT
OF WEBER'S LAW. § III. PSYCHOLOGICAL INTERPRETATION OF THE
LAW.

§1

FOR the solution of all the problems which may arise in
any definite sense-department, there are required, as we
have seen, two kinds of measurement. First, we must
know the constant relation in which alteration of sensation-
intensity stands to alteration of the intensity of stimulus ; and,
secondly, the magnitude of the just noticeable sensation must
be determined. The first of these measurements we have
carried out ; the second now remains to be performed.

Pressure-sensations afford us the simplest conditions for our
investigations. We lay upon that portion of the skin whose
sensibility is to be tested small weights, preferably of cork or
pith, and seek to ascertain what magnitude of weight is
necessary for the production of a just noticeable sensation.
Observations made in this way have shown that the sensibility
of the skin at different parts of its surface is very far from being
uniform. The most sensitive portions are the forehead, temples,
eyelids, the outer surface of the fore-arm, and the back of the
hand. We can usually sense on these parts weights of only
.g-i-3- gramme. Less sensitive are the inside of the fore-arm, the
cheeks, and the nose, and very much less sensitive than these
the palm of the hand, the abdomen, and the thigh. Here the
sensibility sinks to about -fa gramme. On some specially
protected parts, — e.g., the nails and the heel, — the just noticeable
weight rises as high as a whole gramme.

Far more adequate for the apprehension of weak stimuli is
our organ of hearing. A mere touch of the external auditory

The Just Noticeable Sensation 51

meatus or any contact with the tympanic membrane excites, as
we all know, a fairly strong sound-sensation. And even a distant
sound must be very weak indeed to be imperceptible. In
making observations for the determination of the limit of
auditory sensibility, we must, of course, never forget to take
into account all the conditions upon which the intensity is
dependent. If, e.g., we measure the sensibility of an ear by the
sound produced by a falling weight, we must know, not only
the magnitude and material of the weight, but also the material
of the body upon which it falls. And we must, further, de-
termine the rapidity of its fall and the distance of our ear from
the place where the sound is produced. It has been discovered
that a normally sensitive ear can just sense the sound made by
a cork pellet, weighing I milligramme, in falling through a
height of i millimetre, at a distance of 91 millimetres. That
we may expect to find considerable difference in different
individuals is a matter of course, justified by our everyday
experience. Diseases of the sense-organ affect our hearing ;
and, in addition to this, as old age draws on, the acuteness of
this sense usually declines, passing through the most various
stages from hardness of hearing to complete deafness — one
of the commonest defects of sense.

If we are to use the sound-magnitude which we have just
determined as a unit of stimulus, we must be able to compare
with it the intensity of all other sounds which are employed as
stimuli. The comparison is not difficult. Given the sound
whose intensity is to be measured, we need only to remove it
to the distance at which it just disappears. It is then precisely
as great as the sound made by a cork weighing I milligramme,
falling through a height of I millimetre upon a sheet of glass,
at a distance of 91 millimetres from the ear. That distance
tells us at once how many times greater the given sound at the
place of its production is than the just noticeable sound-
intensity. An ordinary musket-shot is just audible at a
distance of 7,000 metres. This distance is rather more than
70,000 times as great as the distance 91 millimetres. Since the
intensity of the sound decreases as the square of the distance,
it follows that the sound-intensity of the musket-shot is more
than 4,900,000,000 times that of the cork pellet which we

52 Lectures on Human and Animal Psychology

adopted as our unit. A similar comparison with the unit may
be carried out for any other sound. We could easily determine,
e.g., how many sensation-units are comprehended in a definite
stroke of the sound-pendulum (p. 30). And since we can
easily take the next step, and compare the various sound-
intensities with one another, it is perfectly possible to express
intensities of sound by means of a single scale like that which
we used for weights. There is only one condition which we
must be careful not to disregard : we must never make an
observation while other noises are affecting the ear, or while the
movement of the air renders the propagation of sound irregular.
The quiet of night is therefore especially suitable for the
experimental measurement of sound-sensations.

The conditions are different when we are dealing with the
sense of sight. It is obvious that we can only attempt to
determine the just noticeable sensation, if there is possible for
the sense-organ a state of absolute inactivity, during which
there is no sensation whatever. This condition is realisable for
the ear. We clearly distinguish noise from silence, as a state
of things where auditory sensations are wanting. The corre-
sponding distinction for the eye would be that between dark
and bright. But visual darkness is something quite different
from auditory silence. By greatly diminishing the intensity of
light we may obtain darkness without there necessarily being
any actual disappearance of the external light. Or if we close
our eyes we are also in darkness ; but it does not follow that
we are completely destitute of light-sensations. In nearly
every case, a certain amount of external light penetrates to the
closed eye. And not only that, but the closing of the eye is
the cause of a light-sensation, the pressure on the eyeball
serving as a retinal stimulus. You may easily convince your-
selves of this by making the pressure somewhat stronger ; the
weak shimmer which you still see, though you have closed your
eyes, is thereby intensified, till finally the whole of the darkened
field of vision is flooded by a sea of light.

But even in the absence of this mechanical stimulus, and
even in the darkest night, our eyes are never free from light-
stimulation. With a little attention we can see that the dark-
ness deepens and lifts, gives place here and there to a brighter

The Just Noticeable Sensation 53

twilight, which is in its turn followed by a still denser black-
ness. We can even persuade ourselves at times that we re-
cognise the blurred outlines of external objects ; now and again
a brilliant flash of lightning seems to irradiate the shadows.
So that the eye is always active, however complete the dark-
ness, and we may easily find ourselves doubting whether it is
due to a light from our eye or from the night itself that we
are able to see. But we may readily convince ourselves that it
is no external light which we have to thank for these phenomena
of light and darkness. If we move, they accompany us ; they
correspond to no external object ; they persist though we have
assured ourselves with all possible care of our complete isolation
from external light. But more, not only this changing shimmer
which we observe in the dark, but even the deepest black
that we can see, is always a light-sensation. When we close
our eyes, our darkened field of vision possesses the same form
as the bright field of the open eye. All that lies within the
limit of this field we see black ; whatever lies outside of it
we see not black, but not at all. When it is daylight, and our
eyes are open, we do not say that the objects behind our back
appear black to us. So that the blackest black which we can
see is our weakest sensation of light. To sense this is not the
same as to have no sensation whatever. And it follows that
there are degrees of darkness, as of light ; that there are
differences of blackness, that we may pass gradually from the
deepest black to a brighter, from that to grey, and so finally
to white.

We see then that the view of the ancients, that the eye is
itself the source of light, is not without a certain foundation.
Only we can never see and recognise external objects by means
of this light. The light-sensation which we have in the dark
is caused by a stimulus within the eye. But if we are to see
objects, the light-stimulus must proceed from them. That
there should be a continual excitation of a sense-organ is
certainly a peculiar state of things, probably not occurring else-
where ; but it becomes intelligible when we remember that the
eye is by far the most sensitive of the sense-organs. A stimulus
which is not nearly strong enough to occasion a sensation of
hearing or of pressure is considerably more than just noticeable

54 Lectures on Human and Animal Psychology

for the eye. In this latter case the normal physiological con-
ditions of the organ may very probably furnish the occasion
for a sensation ; the chemical processes which constitute nutri-
tion may possibly serve to stimulate the neural epithelium of
the eye. Less constant stimulation is caused by the pressure
exerted upon the eyeball by the muscles which move it. This
stimulus will always be operative even in rest, since the muscles
are never entirely relaxed ; but it increases in intensity during
movement. We can observe the same phenomenon in the
light-sensations which we have in the dark. They, too, become
more intensive when the eye is moved.

It is now self-evident that the conditions of vision prevent us
from measuring the magnitude of the stimulus which corre-
sponds to a just noticeable light-sensation. The eye always has
a sensation which is more than just noticeable, and all stimuli
which affect us can, therefore, simply increase the intra-ocular
light-sensation which is inevitably present. It only remains for
us in this case to determine the least light-intensity, which is in
absolute darkness just noticeably brighter than the black of the
field of vision. We can most easily obtain very weak light-
intensities of this kind by passing a constant current through
a metal wire. As we increase the intensity of the current, the
wire becomes hotter and hotter, till at a definite temperature it
begins to be luminous. And since we can graduate the strength
of a galvanic current at our pleasure, the intensity at which the
luminosity of the wire becomes just noticeable can be readily
determined. We have then only to compare its objective value
with that of other known light-intensities. It has been found
in this way that the just noticeable intensity of light is approxi-
mately 3-^5- of the light of the full moon reflected from white
paper.

The investigations to which we have referred furnish us ap-
proximately with our units of sensation and stimulus for
pressure, sound, and light, though in the latter case with the
limitation rendered necessary by the existence of the intra-
ocular light No successful attempt has yet been made to deter-
mine these units for the other sense-impressions, — for taste, smell,
and temperature. This is partly due to the fact that we are not
able to control the operation of stimuli in these departments

The Jiist Noticeable Sensation 55

with sufficient accuracy ; and it is in part caused by the general
impossibility of putting the organ into a condition of total free-
dom from stimulation, a condition, — that is, which would corre-
spond to the zero-point of our stimulus-scale

Now that we have determined in this way the just noticeable
stimulus- difference and the just noticeable stimulus-magnitude,
the two magnitudes upon which our measurement of sensation
depends, there arises a further question : do these two magni-
tudes stand in any definite relation to each other ? If our
sensibility to stimulus shows a certain variability, will not also
our sensibility to stimulus-difference be variable ? We saw that
this latter is expressible by certain constant fractions ; that, e.g.y
our sensibility to differences of pressure is •£, to differences of
light is YJ^J- : in other words, that a pressure must be increased
by •£ of its magnitude, a light by yj^- of its intensity, if the
difference is to become noticeable. Are these relations really
constant, as we have asserted ; or is it not rather highly probable
that they vary with variations in sensibility ?

Obvious as it may appear to answer the latter question in the
affirmative, more careful reflection will at once convince us that
the opposite is to be expected if the general law of the depend-
ence of sensation upon stimulus holds. This law informs us,
you remember, that a stimulus, whether great or small, must
always increase in the same ratio, in order to condition a defi-
nite sensation-difference. Suppose, therefore, that the sensibility
of some sense were, in an exceptional case, reduced by one-half.
It would then, of course, be necessary to take twice as great a
stimulus as before in order to occasion a noticeable sensation ;
and if we wished to increase this sensation again by a noticeable
magnitude, the larger stimulus would naturally need, as the law
says, a relatively greater increase. But there is not the least
reason for supposing that this increase must be greater than the
proportion originally required.

This hypothesis is completely confirmed at every point by
observation. If sensibility has changed, every stimulus is sensed
more or less intensely than before ; but if two stimuli are com-
pared, their difference is just as great in sensation as it was pre-
vious to the change. If the sensation I is doubled, the sensation
2 is also doubled. If a stimulus I had to be increased by ^ to

56 Lectures on Human and Animal Psychology

alter sensation, then when, on account of the decrease of sen-
sibility, the stimulus 2 must be substituted for it in order to pro-
duce the same sensation, this latter stimulus must be increased
by |-, if sensation is to be altered, etc. In short, sensibility to
stimulation does not affect in any way the law of dependency of
sensation upon stimulus.

§ II

We may now return to the point from which we set out. Our
object was to investigate the dependency of sensation upon
stimulus. Stimulus, as the physical process directly parallel to
the sensation, means here of course the internal stimulus, opera-
tive in some sensory centre of the brain. But, to make our
problem easier, we began by investigating the dependency of
sensation upon external stimulus. The time has now come for
raising the question whether it is at all probable that the trans-
lation of external into internal stimulus has in any way influenced
the connections which we have found. We have, in fact, already
seen that stimulation- processes are only set up in the sense-
organs and nerves when the external stimulus has attained to a
certain intensity ; and since it is not until this process reaches
the brain that it is immediately accompanied by sensation, a
stimulus which is weaker than this is naturally the same to us as
no stimulus at all. On the other hand, it is equally conceivable
that the internal stimulation-process must have reached a definite
intensity before it gave rise to a noticeable sensation.

As a matter of fact, there can be no doubt that both these
conditions are realised. It is a necessary consequence of the
more or less protected position of the sensory nerves and their
peripheral end-organs that exceedingly weak stimuli cannot
affect them. And it is just as certain that the stimulation-
process in the brain is only perceived by us at a certain intensity.
This is sufficiently obvious if we consider the causes which
condition change of sensibility. If we direct our attention to the
impressions of any sense-organ, we can apprehend much weaker
stimuli than is the case when our attention is first aroused
through the force of the impressions themselves. But it is not
probable that the conditions of conduction to the brain have

Upper and Lower Limit of Weber s Law 57

altered in the two cases. We are always subject to a large
number of external impressions, but only a few of them are
perceived by us. Nevertheless it is true that these impressions,
acting jointly, are capable, unless they are very weak, not only
of exciting the sensory nerves, but of passing along them to the
central organ.

Now, just as there is a lower limit, below which the external
stimulus is too weak to occasion an internal stimulation, may
there not also be an upper limit, above which it is impossible to
arouse any stronger neural excitation ? If this is so, we shall
expect to find that the law which is valid for moderate stimuli
does not hold in the case of the strongest.

As a matter of fact, it may easily be proved that neural
excitations can never be increased beyond a certain point. The
preservation of the nerves and their end-organs renders this
necessary. If we stimulate the eye with stronger and stronger
light, we shall at last injure the power of vision, or, indeed,
entirely destroy it. The processes in the sensory nerves depend
upon the constant renewal of the substances provided by the
blood. The more intensive the sensory "processes, the more
energetically must the renewal be attended to. And since this
cannot go on indefinitely, it is evident that the intensity of the
neural processes has also its limit of increase. We do not as a
rule reach this limiting point suddenly in the process of stimula-
tion, but rather approach it gradually. At first the neural
process increases in intensity in direct proportion to the external
stimulus ; later this increase becomes somewhat slower ; finally it
ceases altogether, however much we may continue to increase
the intensity of the stimulus. We must, therefore, necessarily
expect that the relation of the just noticeable sensation-difference
to the total magnitude of stimulus is in reality not altogether
constant, but slowly varies with the gradual increase of stimulus.
If, e.g., a moderate pressure upon the skin must always be
increased by -|-, a very intense pressure will require a somewhat
greater increase ; and finally there will be a certain sensation of
pressure an increase of which is absolutely impossible, however
heavy the weights we place upon the stimulated part.

Many phenomena of our everyday life are to be explained on
this principle. It is well known that extreme pain admits of no

58 Lectures on Human and Animal Psychology

degrees or distinctions ; that a very intense light blinds us ; an
excessively loud sound deafens us. But the possibility of sensa-
tion-increase does not cease abruptly, but by degrees. If we
compare the shadow thrown by an object in moonlight with the
shadow cast by the same object in sunlight, it will be at once
seen that the former appears much darker than the latter. In a
landscape seen by moonlight, this stronger contrast of light and
shade makes the illumination far brighter, although it is absolutely
much less intense. And from this fact we can distinguish at the
first glance whether a picture represents a moonlight or a day-
light scene. It is not in the power of the artist to mark this
difference by an absolute difference of light-intensity. Both his
paintings are equally bright; but he makes the difference between
light and shadow greater in the first picture than in the second,
and by this single device enables us to distinguish in a moment
the night scene from the day scene. This device would be
impossible if it were exactly and invariably true, as our law puts
it, that an equal sensation-difference always corresponds to an
equal difference-relation of light-intensity. For our two land-
scapes are a case in point. The moonlight shadows differ from
moonlight by a quantity of light which is relatively to the in-
tensity of the moonlight just as great as that separating the sun-
light shadows from the sunlight ; so that the light-intensity of
the moonlight shadows stands to that of the sunlight shadows
as moonlight to sunlight. Nevertheless the light of the moon
appears much brighter in relation to its shadow ; i.e., the sensa-
tion-difference is greater here, where the light-stimulus is less,
than it is in the case of sunlight, where the light-stimulus is more
intense.

All the various influences which condition divergences from
the simple law of the dependency of sensation upon stimulus
have proved to be due to the intermediary processes of neural
excitation. And it is a justifiable assumption that the law is
literally valid as between internal stimulus and sensation. So
that if we were able to measure directly the intensity of the
stimulation-process in the brain, instead of the external stimulus,
we should find the law holding without exception. In investi-
gating the relations of sensation to stimulus, we have, as a
matter of fact, been observing the effect of two laws : the law of

Psychological Interpretation of the Law 59

the dependency of internal upon external stimulus, and the law
of the dependency of sensation upon the former class of stimuli-
If we suppose that the intensity of the internal stimulation*
remains within certain limits proportional to that of the external
stimulus which occasions it, but that, as the external stimulus
continues to increase, it increases more and more slowly, we
have a simple explanation of the deviations from the law of the
logarithmic relation between stimulus and sensation. We have

o

been unable to investigate this relation without the constant
intrusion of the nervous excitation, — an intermediary which has
unfortunately remained hitherto inaccessible to the method of
exact physiological examination.

And now we approach the final question which is suggested
by a consideration of the law of the dependency of sensation-
intensities : the question of the psychological interpretation of
the facts which we have hitherto ascertained.

§ HI

The discovery of a law only becomes of cardinal importance
when we have learned to know its connections. The relation
between sensation and stimulus is of importance because the
knowledge of it allows us for the first time in the history of
psychology to apply principles of exact measurement to mental
magnitudes. But this measurement will not have its proper
value until we have learned in what peculiarities of sensation, o*
of the organ which transforms the stimulus into a sensation, the
law has its basis. Is the relation physically conditioned by
processes in the nervous system ? Or is it psychically condi-
tioned by the nature of the mind ? Or, finally, does it express
the interconnection of the world without and the world within,
which is conditioned by both these factors ? Is it, in a word, to
be explained in terms of psychophysics ?

It has been often assumed that our law possesses only a
physiological significance. As the stimulus, even in acting upon
the external sense-organs, must have reached a certain intensity,
if it is to cause an excitation in them, this process of excitation
will perhaps meet with increasing obstacles in the sensory
nerves, but especially in the central organ. May not now, it is

-6O Lectures on Human and Animal Psychology

said, these central obstacles increase with increasing stimulation
just so that finally, in the sensory centre, where alone the pro-
cesses of stimulation are sensed, the magnitude of the stimulation
is only proportional to the logarithm of the external stimulus ?

As yet this conjecture can neither be proven nor contradicted.
For we know almost nothing regarding the law of the trans-
mission of stimulation-processes in the brain. Considered more
closely, however, it falls into two hypotheses. According to the
first of these, it should result from a comparison of the internal
stimulation-processes in the sensory centre with the external
stimuli, if such a comparison were possible, that the former
does not increase in direct proportion to the latter, but more
slowly ; and in such a way that the logarithmic law of depend-
ency arises. This view seeks support in the general postulate
of the parallelism of mental and physical processes, according
to which the bare fact of the logarithmic increase of sensation-
intensities requires that the physical processes in the brain,
corresponding to the sensations, shall also behave as these latter
behave. According to the second hypothesis, this behaviour is
the result of the gradual decrease of the intensity of the stimula-
tion-process during its propagation through the central organ.
We shall hardly find any facts that can be adduced in favour of
this latter assumption. At any rate, what little we do know of
the propagation of stimulation in the central organ (e.g., the
laws of reflex movement, when the intensity of the stimulation
is increased) speaks rather against than for it. Moreover, we
cannot regard the hypothesis as probable, even if we grant
the applicability of the law of psychophysical parallelism to the
present case. To imagine that the processes of sensation, of the
.apprehension of sensation, and of its comparative measurement
'depend on their physical side on a simple transmission from a
sense-organ to a definite part of the brain is to have a very
crude and inadequate idea of that principle. It is surely plain
that the different degrees in the clearness and relative notice-
ability of sensations are secondary sensation-characteristics,
which must occupy the most important place in any explana-
tion of Weber's law. And there must be certain physical
processes running parallel to these characteristics, if that law is
to be physiologically interpreted. But mental processes of so

Psychological Interpretation of the Law 61

complex a character would necessarily be paralleled by complex
physical concomitants, — by the complicated interaction of various
central areas. Only by their means could justice be done to the-
fact, expressed in the law, of the relative decrease of stimulation,
with absolute increase of stimulus-intensity. However, be this as
it may, no unverifiable hypotheses of this kind should prevent us-
from raising the question whether it is not also possible to dis-
cover a psychological interpretation. This would have to take
its place alongside of the physiological, just as the physical and-
mental processes themselves, as we have seen, are parallel and
not mutually dependent.

This latter consideration tells equally against the third of the
interpretations of Weber's law which we mentioned above, — the
psychophysical. According to this view, neither physiological
nor psychological conditions suffice for the establishment of the
law. It is rather to be regarded as a specific principle of the
interaction of physical and psychical, a fundamental law which
as such is not capable of any further explanation.

We must urge, in the first place, that it is extremely difficult
to conceive of the existence of a law of this kind. It belongs
neither to the one territory nor to the other, but only to their
borderland ; and it disappears when we leave that on the one
side or the other. It seems as though such a hypothesis must
inevitably take us back to the spiritualistic doctrines which
proved so unfruitful for the explanation of the facts of mental
life, — those which regarded bodily and mental existence as two-
generically distinct modes of being, whose interconnection is
merely external. We shall, therefore, decline to adopt this
theory of mutual influence, which explains nothing, unless
we find that a physiological or a psychological explanation
is impossible. But we must remember that it was through
the observation of psychological facts, of sensations, that the
law was discovered. It is, therefore, only natural that we should
ask for a psychological interpretation of it. The physiological
interpretation must remain at present a general postulate, be-
cause a relation of external to internal stimulus, like that ex-
pressed by the law, is as yet only a matter of hypothesis based
on the principle of psychophysical parallelism, and can by no
means be proven. As a matter of fact, we shall see as we pro-

62 Lectiires on Human and Animal Psychology

ceed that the view which makes our law a psychical uniformity
is supported by many other phenomena of our mental life. A
psychological value is assured to it by its actual universality.
But more than that, we are also able to show its dependence
on definite psychological conditions which are everywhere
valid.

What the law tells us, first of all, is simply this : that our
sensation furnishes no measure of absolute, but only of relative
magnitudes ; or, in other words, that we can only estimate
magnitudes by comparison. If an excitation of a pressure-
nerve is increased from the intensity I to i£, this is the same as
if an excitation of the intensity 2 were increased to 2f. The
two differences are equal, if we compare them in ignorance of
the absolute intensity of the two excitation-processes. We
possess no mental measure whatsoever of absolute mental
magnitudes. We are no more able to conceive of an absolute
magnitude of sensation than we can have an idea of absolute
time-magnitude, or of any other magnitude of a mental nature.
It is well known that we continually make mistakes in estimat-
ing absolute distances with the unaided eye, without the assist-
ance of instruments of measurement, — whereas the eye is an
exceedingly accurate instrument for estimating differences of
distance. And the same holds in every case where we are re-
stricted to the means with which nature has provided us : we
can only measure relatively ; we can only compare the magni-
tudes which are directly given us.

Measurement of sensation in general is rendered possible
simply and solely by our reference of all qualitatively similar
sensations as regards their intensity to an arbitrary sensation-
unit. We cannot compare all possible intensities at once with
one another, and in this way refer them to the unit which we
have chosen. That method of procedure is excluded by the
very notion of comparison. In the first place, we can only com-
pare individual things. We can, therefore, never unite more
than two units of sensation in a single comparison. We re-
present to ourselves first one and then the other of these in-
tensities, and so determine which is the stronger sensation. We
can only pass to a third sensation, and estimate its intensity by
comparing it with one of the two sensations which have been

Psychological Interpretation of the Law 63

already compared. In this way it becomes possible for us to
bring a large number of sensations into one continuous series.
We can only do this by proceeding successively from sensation
to sensation, from comparison to comparison. But if we can
never compare simultaneously more than two, never three or
more, magnitudes, the consequence is obvious that our measure
of sensation is relative, i.e., is always limited to a determination
of the ratio in which two sensations stand to each other. It is
no argument against this relativity to urge that we can always
proceed to new comparisons, and so measure all possible in-
tensities ; for the series thus obtained is still only composed of
individual comparisons. In fine, then, this law of the logarithmic
relation of sensation to stimulus is a mathematical expression
for a psychological process of universal validity.

But in saying this we have already answered the question
which we left undecided when we entered upon our considera-
tion of the measurement of the intensity of sensation. The fact
that the more intensive stimulus requires a greater addition for
the production of an equally noticeable sensation-increase ad-
mits, as we saw, of a twofold interpretation. Either the more
intensive sensation demands the operation of a more intensive
stimulus for its increase by an equal sensation-magnitude, or the
more intensive sensation demands a more intensive sensation-
increase, if this latter is to appear equally noticeable. Our
reference of Weber's law to the principle of the relativity of
sensations favours the second of these interpretations. Our
comparison is always relative. In order that a more intensive
sensation-magnitude may increase by as much as a lesser sensa-
tion, the sensation-increase must be correspondingly greater ;
and two sensation-increases which lie at different parts of the
sensation-scale will be equally noticeable when they stand in
equal relations to the stimulation-intensities to which they are
added.

LECTURE V

I. QUALITY OF SENSATION ; GENERAL REMARKS UPON THK SENSA-
TIONS OF PRESSURE, TEMPERATURE, TASTE, AND SMELL. § II. TONE-
SENSATIONS ; BEATS. § III. CLANG-COLOUR; SIMULTANEOUS CLANGS.
§ IV. NOISES. § V. MEASUREMENT OF DIFFERENCES OF TONE-
SENSATIONS ; THE TONAL SCALE ; RELATIONS TO WEBER'S LAW.

T^HE intensity of a sensation is only one side of it. Not
only has every sensation its own intensity, but also a
definite quality which renders it distinguishable from other
sensations.

The most extreme instances of qualitative difference are
furnished by the sensations of the different sense-organs, — sensa-
tions of eye, ear, and skin. A colour and a tone, a sensation
of pressure and one of warmth, are simply incomparable with
each other. Hence they are denominated disparate sensations.
But qualitative differences are also to be observed within the
sphere of one and the same sense. Thus red, green, blue, and
yellow are entirely different sensations, although they are all
sensations of sight. The one thing that proves a closer inter-
connection among these sensations of a single modality is the
possibility of a continuous passage between any two of them.
the one passing by slow degrees into the other. Thus red may
pass into green, or a low into a high tone. So that the
relation between two different sensations within one sense is
analogous to that between two points which lie within one and
the same spatial continuum ; while two disparate sensations
may be compared to points which belong in entirely different
spaces, and whose position with regard to each other is un-
known.

There is no sense-organ within whose sphere qualitative
differences do not occur in greater or less number. Sometimes

Quality of Sensation 65

those differences are very few, as in the case of temperature,
where cold and hot appear as the only two sensible qualities.
Sometimes the differences are of such a nature that they will
not submit to any definite method of classification. The sensa-
tions of pressure, e.g., obviously present marked qualitative
differences ; an ordinary pressure upon the skin is a very dif-
ferent sensation from the prick of a needle-point or the scratch
from a rough surface. But plain as these differences are, it is
impossible for us to state them in terms of any definite recip-
rocal relation.

Nor are we in a much better position with regard to the
sensations of smell and taste. It is true that certain groups of
odoriferous substances, which are for the most part chemically
related, give rise to similar scents ; e.g., many of the ethereal oils,
the volatile fatty acids, the metals, etc. But we are entirely in
ignorance of the relation in which these various scents stand to
one another.

With taste-sensations we can go one step farther. Here there
can be no doubt that the number of existent sensations is more
limited, and therefore their investigation easier. If we exclude
everything which does not belong to the sense of taste itself,
there remain, it seems, only six sharply differentiated sensa-
tions : sweet, sour, alkaline, metallic, bitter, and salt. In saying
this, we do not mean to assert that these six are the only taste-
sensations possible at all. It is clear that, e.g., by combining
sweet and bitter, we can produce a taste which is neither
sweet nor bitter, although it has something of both qualities.
The result is a mixed sensation, not a qualitatively simple one.
In ordinary life we are apt to think that we possess a far
greater number of taste-sensations. But this is only because
we do not commonly distinguish taste from smell. When we
are tasting, we are smelling at the same time, and so there
arises a combination of smell and taste resulting in a mixed
sensation, which is referred solely to taste simply because our
attention is principally directed to that sense. How much
really depends upon the sense of smell can be readily seen by
recalling a bad cold. In that state we discover with amazement
that many things have absolutely no taste at all. Or, again,
the influence of smell can be still more certainly eliminated by

F

66 Lectures on Human and Animal Psychology

filling both nostrils with water. In this experiment we are
entirely confined to the sensations of taste proper. And we
find that our tongue cognises no more than those six definitely
characterised sensations.

This examination of the sensations of taste serves to show us
the method to be pursued in a more exact investigation of the
quality of sensation in general. In every case our first question
must be, whether there are not discoverable certain sensation-
qualities which are incomparable with one another, and which
are therefore to be regarded as pure and simple. When we
have found these, and definitely established their number for
some particular modality of sense, we have to ask further : what
are the compound or mixed sensations which arise from the
simultaneous occurrence of two or more of the simple ones ?
That is to say, in investigating any given sensation, we adopt a
similar mode of procedure to that which the chemist employs
in the investigation of a given body. We must first determine
the elements of which the sensation is composed, and then go
on to show what relations these elements bear to one another in
the combination. Here, just as in the case of the measurement
of intensity, we have to set out from definite units of measure-
ment. But then, of course, these were units of quantity ; now
we shall be dealing with units of quality. These units are com-
parable to atoms, from which the sensation is built up. But, as
you all know, the term ' atom ' means two different things. For
the physicist it is a unit of quantity, for the chemist a unit of
quality. So that in splitting up our sensations into quantitative
and qualitative units we are analysing these mental states in a
way which recalls the two chief directions of analysis of the
material world without us.

In the case of the sensations which we have had under con-
sideration up to the present time, this analysis into qualitative
units has been either not carried out at all, or only very im-
perfectly. It is quite otherwise with the two senses whose high
degree of functional development has gained for them the title
of the ' higher senses ' : those of sight and hearing.

Tone-sensations; Beats 67

The quality of auditory sensations is given, first of all, with
their pitch. With this is always connected the clang, a peculiar
colouring of tone-sensation. Noise we distinguish from both, as
a sound-impression in which pitch can be perceived either only
uncertainly or not at all.

The simplest of these three forms of auditory sensation is the
pitch, although in reality this can never be separated from the
clang, since it is only in a clang that a particular pitch is per-
ceived. That need not, however, prevent us from disregarding
for the time being everything that gives to a tone its peculiar
clang-character, and attending simply to that property of it
which we call its pitch. Indeed, a psychological analysis of
sensations demands that such an abstraction be made, for its
business is to continue analysing every sense-impression until it
reaches the ultimate elements, which cannot be any further
divided. Now the pitch is easily separable from the other
elements of a musical clang. It may remain unchanged, while
the clang-character of the impression varies. This happens, e.g.,
when we strike the same tone upon a number of different
musical instruments. On the other hand, the pitch may vary
to a certain extent, while the clang-character of the impression
does not change. This happens when we sound neighbouring
tones on the same instrument. When, however, the tonal pitch
of the two impressions is very different, the clang-quality gene-
rally changes with it, as is easily seen by comparing, e.g., two
widely distant tones upon a piano.

It was known to the ancients that tones consist objectively of
vibrations of the sounding bodies and of the air carrying the
sounds. Indeed, in the case of the very deepest tones, these vibra-
tions are actually perceptible by the eye. In the same way the
vibrations of sounding strings can be easily perceived by the
eye. The best means of showing the origin of tones from
vibrations is afforded by the siren, a physical instrument especi-
ally constructed for this purpose. It consists of a disc provided
with a series of circular holes, and moving across a current of
air in such a way that within any given time the current is

68 Lectiires on Human and Animal Psychology

interrupted as often as unperforated por-
tions of the disc alternate with perforated.
By regulating the velocity of the rotation
of the disc we can produce at will high
or low tones. The slowest rate of air-
vibrations which can give rise to the
perception of a tone is about 16 in i",
though under favourable conditions it

may sink to 8. The best means of pro-
FIG. 5. .

ducing these very deepest tones is given

by large tuning-forks or vibrating steel rods. As we approach
the limen of perception, however, the tone becomes so faint that,
however extensive the vibrations, it can only be heard at a quite
short distance. The deepest tones of the musical scale lie be-
tween 32 and 100 vibrations in i". As the number of vibrations
increases the pitch steadily rises. When the vibration- rate has
increased to about 40,000, tone ceases altogether, and we hear
only a hissing noise.

It is only in the case of the very deepest tones, which cannot
be employed for musical purposes, that we are able to distin-
guish the air-beats corresponding to their vibrations. Our
knowledge of the increase of vibration-rate in the case of the
higher tones does not, therefore, depend upon the immediate
perception of the vibrations, but upon another observation,
which is closely related to it. As early as the days of the
Pythagoreans it was a familiar fact that a string shortened to
half its length vibrates twice as rapidly as the whole string ;
that one reduced to a third of its original length vibrates three
times as rapidly, one reduced to a quarter four times, and so
on. Now, the tone of the half-string is the octave of the tone
of the whole string ; the tone of the third part, the fifth of this
octave ; that of the fourth part, the double octave. So that this
law of the uniform relation of the length of a string to its vibra-
tion-rate contains in it another important law, that those rela-
tions of tones which are apprehended as harmonious correspond
to simple ratios of their vibration- rates.

Harmonious relations of tones were originally distinguished
from inharmonious only by the more pleasing character of the
impression which they made in a tone-series. Singing and

Tone-sensations; Beats 69

playing in unison came long before part-singing and harmony.
But as soon as the custom arose of employing several voices of
different register in the rendering of a melody, there came to
light other phenomena, connected with the simultaneous sounding
of tones, and with the consequent simultaneity of air-vibrations
of different velocities. Not only, that is, can we distinguish a
single tone from a clang compound of several tones, but we can
easily hear out of such a clang, supposing that it is harmonious,
the separate single tones which compose it. It is a matter of
direct perception, e.g., that the common chord of c major is
composed of the three tones c eg. Whenever a compound clang
is harmonious, the separate simultaneous vibrations unite to
produce a common movement of the air, itself consisting of very
brief and uniformly recurring r\ f\ f\ f\ f\ f\

periods. Fig. 6 shows this for i-.g V^j \A \A \>|\V/ \>j
the three compound clangs of a
tone plus its octave, its fifth, and
its major third. The points at A /\ /\ r\ f\ /\

which a new period begins are 2:3 j • ! !

indicated in each case by dotted *\J\f\f\J\f\f\j\f\J

vertical lines. In the octave the

two vibration- rates which unite f\ /\/\/~V/\ /\ i

to form the compound clang 4:5 \t\ r\ r\ r\ f\\/\ r\ r\
have in each period the ratio \J \J \J \J \J \J

1:2; in the fifth, the ratio 2:3; FlG- 6-

in the major third 4:5. Similar simple periods are found to recur
in the other harmonious two-clangs ; the ratios of the constituent
vibration-rates are in the case of the fourth 3 : 4, in the minoi
third 5 : 6, in the sixth 3 : 5. Since all these periods of compound
vibration-rates are repeated just as regularly as the periods
of simple vibration-rates, we can understand how it is that a
harmonious compound clang produces upon us as uniform an
impression as a single tone. It is true that we distinguish in it
the presence of more tones than one ; but these unite to form a
total sensation, which runs its course with perfect evenness.

But it is quite different when two tones are sounded together
whose vibration-rates do not stand in any simple and harmonious
ratio, but bear a more complex relation to each other. In such
a case there can be no production of the uniform periods,

70 Lectures on Human and Animal Psychology

recurring at very brief intervals of time, which we have found in
the harmonious compound clangs. As a result of this, the inter-
action of the vibrations causes a disturbance in the uniform
course of sensation. Wherever two movements in the same
direction coincide, as at a and b (Fig. 7), they strengthen each

other ; and where two
coincident movements
have an opposite direc-
tion, as at in, • they

<* ^ weaken each other. It

FIG. 7. j , c

depends, of course, on

the difference of vibration-rate, how often these pendular to-and-
fro movements of the air particles agree or disagree with each
other. If one tone makes exactly one vibration more in i"
than another, there will occur in each second one such increase
and decrease. For if at the beginning of the second, at a, both
vibrations start at the same stage, there will meet in the middle
of the second, at m, a forward movement of one wave and a
backward movement of the other, so that the two cancel one
another ; while again at the end of the second, at £,they will be
travelling in the same direction, and will, therefore, assist each
other. It is clear that just the same will happen if the difference
of the two tones is one of a greater number of vibrations ; there
will be as many increases and decreases, as many beats, as there
are more vibrations in the one case than in the other. If the
difference is very small, amounting, e.g., to one vibration in the
course of several seconds, it will be scarcely noticed, the
diminuendo and crescendo of the tone occurring continuously and
gradually. If the change is spread over a sufficiently long space
of time, it will not be perceived at all. But if one or more beats
occur in i", they are clearly noticeable ; and if their number
increases to 10 or more, their quick succession will be sensed
as a very unpleasant whirring.

The limit of rapidity at which the beats of dissonant tones
may be perceived cannot be determined with any degree of
certainty. For, in the first place, the beats, as they follow one
another faster and faster, give rise to a general impression of
harshness, more or less comparable to that which a rough
surface produces in the sense of touch ; and when the rapidity

Tone-Sensations : Beats 7 1

becomes still greater, while the tones are not heard as a
harmony, the beats and even the roughness of the clang also
disappear. The extreme limit at which this harshness can still
be distinguished appears to be reached in the neighbourhood of
60 beats in i".

Now these observations upon inharmonious compound clangs
seem to imply a contradiction between the perception of the
beats and the laws which we formulated above in terms of
the vibration-rates of tones. For it is found that tones can still
give rise to clearly perceptible beats when the difference between
their vibration-rates amounts to considerably more than 60 in
i". If we take, e.g., the two neighbouring tones c and d from the
lower or middle region of the scale of pure temperament, and
strike the clangs together, we shall obtain loud beats. This is
perfectly intelligible from what has been said above. For if the
tone c makes 128 vibrations in i", d, which is higher by the
interval of a second, will make 9/8 x 128, or 144 vibrations
The two tones must, therefore, give 16 beats in i". But if we
strike with c, not the d, but the octave d\ we are giving a tone
of 2 x 144, or 288 vibrations. Its difference from c amounts to
1 60 vibrations. Yet although it is quite impossible to hear beats
which follow one another as quickly as that, the compound
clang is not merely inharmonious, but is also clearly accompanied
by beats similar to, if not quite so strong as, those arising from
the striking of two notes which are a single whole tone apart.
What reason is there for the fact that the higher tf makes beats
with c, while the tones c or g, octave or fifth of the purely
tempered scale, the differences of whose vibration-rates from
that of c are smaller, give no noticeable beats at all ? The
reason may be discovered from the following simple experiment.

When we strike a piano or guitar-string that is stretched over
the sounding-board, the result is, of course, a tone. If a bridge
is placed in the middle of the string, so that only half of it can
vibrate, the resulting tone rises, as we have said, an octave
higher. By striking first the fundamental, and then the octave,
we come to see that the latter was really contained in the former;
that it sounded, though weakly, along with the fundamental. The
case is the same if first the whole string, and then one-fourth
of it, is struck. Here the double octave is seen to be sounded,

72 Lectures on Human and Animal Psychology

though very weakly, with the fundamental, and so on. If we
have trained our ear in the comparison of clangs, we are able to
hear out these higher tones, the over-tones, from the fundamental
It is found that every tone of our musical instruments and of the
human voice contains a large number of over-tones; so that
strictly speaking, we never have the sensation of a simple tone,
but always that of several simultaneously sounding tones, one
of which, however, the fundamental, is so much stronger than the
rest that we usually fail to hear them. The phenomenon of over-
tones finds its physical explanation in the fact that, in most
forms of tonal stimulation, the wave-movement set up in the air
is a compound one. When the string is struck, e.g., not only
does it vibrate in its entire length, and so transmit the ground-
tone to the air, but either half of it vibrates also, though not so
violently, on its own account, and so produces the octave. In
the same way each third and each fourth of the string vibrate ;
thus giving rise to the third of the higher octave, the double
octave, and so forth in decreasing series. These separate tones
persist just as independently of one another as if several instru-
ments were sounding at the same time. The only difference
consists in the greater weakness of the over-tones.

And now we are able to explain the very curious fact that the
tone c beats not merely with the neighbouring d, but also with
the d of the higher octave. Simultaneously with the funda-
mental c there is given the octave c, and this beats with the d,
vvhich stands next to it. The beats are certainly not so pro-
nounced as if the c had been directly sounded, partly because
the over-tone is weaker, partly because the beats follow one
another more quickly; but they are clear enough to be heard.

This simultaneity of fundamental and over-tones is of im-
portance not merely as throwing light on the consonance and
dissonance of the tones in a compound impression, but also as
influencing our apprehension of separate tones. The tones of a
musical instrument and of the human voice are characterised
not only by pitch, but also by a definite clang-character. If all
tones depended simply upon the vibration-rate which determines
their pitch, then, apart from the noises that may chance to
accompany them, every tone of the same pitch would possess
the same character, however it might be produced. This, of

Clang-colour ; Simultaneous Clangs 73

course, is not the case. The same tone sounds quite differently
when given by flute, violin, clarionette, organ, etc. The vibra-
tion-rates must have still other properties, varying for one and
the same tone with the source of sound. As a matter of fact,
we have found the over-tones regularly accompanying tones, and
presenting differences which depend upon the mode of origin of
clangs. There are tones in which scarcely any over-tones are
noticeable. Those of the flute-pipes of an organ come very
near to absolute purity, and those of a tuning-fork standing
upon its resonance-box nearer still. If the resonance-space is
exactly fitted to the primary tone of the tuning-fork, all the
secondary tones are so weak in comparison that they are not
heard as the tone rings off. On the other hand, wind and string
instruments and the human voice always allow a large number
of over-tones to be heard beside the ground-tone. As a general
rule the intensity of the over-tones decreases with their height.
The octave can be heard more clearly than the double octave,
this than the third, etc. But there are considerable differences
in the different instruments. Sometimes the higher octaves
sound most strongly, as on the piano ; sometimes the higher
fifths and thirds, as in the clarionette ; sometimes the first over-
tones are heard at a comparatively uniform intensity, as on the
harmonium ; and sometimes single very high over-tones are
preferred, as in the trumpet and trombone.

We have now inquired into all the conditions of the peculiar
colouring of the different kinds of clangs. This depends partly
upon the intensity of the over-tones in general, partly upon the
character of the strongest among them.

§ III

If the laws of concurrent vibrations which we have been
discussing are true, no tone is ever entirely free from over-tones.
Even though it should be so objectively, there would probably
still attach to it subjectively some kind of clang-colour, due to
the presence of very weak over-tones caused by the concurrent
vibrations of Certain parts of the auditory organ, attuned to the
particular tone.

The tone-sensation which, in virtue of its attendant partial

74 Lectures on Human and Animal Psychology

tones, is possessed of a definite clang-quality, we call a clang \
the particular clang-quality produced by the over-tones, clang-
colour. Every clang consists, therefore, of tone-pitch and clang-
colour, the latter component being in its turn made up of 3
number of weaker tone-sensations accompanying the primary
tone. The clang, that is, is a compound sensation, and since all
tones are in reality clangs, our tone-sensations are never given
in any other than a compound form. We can separate out the
individual simple pitches only by either subjectively abstracting
from the attendant secondary tones in the clang, or strengthen-
ing the primary tone to such an extent that they disappear, as
happens when a tuning-fork vibrates on its resonance-box. But
even if a tone is comparatively rich in secondary tones, we
apprehend it in idea as perfectly unitary and relatively simple,
as is shown by the fact that we ascribe to it only a single pitch.
Over-tones, on the other hand, even though they are strong
enough to be clearly perceived, are not apprehended as separate
pitches, but appear merely as a peculiar modification of the
principal tone. It is plain that this cannot be explained simply
in terms of the lesser intensity of the secondary tones. But it
becomes intelligible when we consider that wherever definite
simple sensations are given in constant connections these
connections blend to form unitary ideas ; and that when it is a
tone that is connected with harmonious secondary tones this
blending process must be very materially furthered by the possi-
bility of the co-existence, without mutual disturbance, of har-
monious vibration-rates. Regarded from this point of view, the
clang-idea presents to us a simple and typical example of a
psychological process which we shall frequently meet with, for
the most part in a more complex form, — the process of sensation-
fusion. All the elementary constituents in this fusion-process
have lost the character which they possessed in their isolated
condition ; in the stable connections into which they have
entered they are determined by the character of the other
elements present. Thus the octave c' of a tone c, when it appears
in the first over-tone of the latter, is something entirely different
from what it is when sensed alone. In the latter case it would
be an independent tone ; in the former it is perceived directly in
its relation to the simultaneously given principal tone, and, since

Clang-colour ; Simultaneous Clangs 75

this is much the stronger, appears as a mere modification of its
clang-character.

The compound clang is distinguished from the simple clang
only by the number and relative intensity of the tones which
enter into it. If we strike the chord c e g, we are sounding three
tones which form part of the series of over-tones belonging to a
lower C. The major third c e corresponds to the proportion of
vibration-rates 4:5; the fifth eg, to 2 : 3 or 4 : 6. That is, the
three tones occupy the fourth, fifth, and sixth places in the
complete tonal series of a simple clang: I, 2, 3, 4, 5, 6, . . .
But while in a single clang these tones appear only as secondary
tones of a lower fundamental, whose clang-colour they determine,
in the second they constitute the chief elements in the whole
impression, and are of equal intensity. In the compound clang,,
therefore, we sense at once a plurality of tones. Since compound
clangs are only harmonious if the ratio of their vibration-rates
is one of simple whole numbers, -they may be regarded in every
case as intensifications of the separate members of the tonal
series of a single clang.

But there is still another element in compound clangs. It
consists in the appearance of lower tones, which are in harmony
with the principal tones, and play a part in the determination of
the character of a compound clang similar to that of the over-
tones in the clang-colour of a single clang.

Whenever there are set up simultaneously two harmonious
sound-waves, whose vibrations strengthen and weaken one
another alternately, at short and uniformly recurring intervals,
there arises from this interaction a new tone, the vibration-rate
of which corresponds to the difference between the vibration-
rates of the two original tones. Look for a moment at the
second pair of curves in Fig. 6, representing the fifth, eg. During
two vibrations of the first and three of the second tone, there is
one coincidence of hill and valley and one each of hill with hill
and valley with valley. So there is set up a third wave-move-
ment, which makes one vibration for every two of the first or
three of the second tone. Such tones, which may be called
either under-tones from their relation to the over-tones, or
difference-tones, from the relation of their vibration-rates to those
of the original tones, may be intensified in complex chords by

76 LectiLres on Human and Animal Psychology

the fact of several of them falling upon the same note. In the
chord c eg, for example, in which the vibration-rates of the tones
stand in the ratio 4:5:6, both c and e, and e and g, produce
the same under-tone i, — a c lying two octaves below the lowest
tone of the chord, — while c and g give a tone 2, i.e.t a c only one
octave below it. 1

To these harmonious under-tones, which we have found
accompanying the compound clang, must always be added the
over-tones of the single clangs. They may also strengthen one
another in certain cases, where different clangs have similar
terms in their series of partial tones. So that every chord, even
the comparatively simple, is made up of a very large number of
sensation-elements, some of which, the more intensive primary
tones, stand out as clearly distinguishable qualities, while the
others merely serve to determine the clang-character of the
chord. The triple clang c e g, for instance, gives us the
following tones : —

Under-tones.

Principal tones.

Over-tones.

G! C

c e g

cl el £ p ^ ^

^ g_

I 2

4 5 6

8 10 12 15 T6 18

20 24

The first over-tones are usually the strongest ; only these are
•entered in the schema. Under-tones which appear as difference-
tones of more than one two-clang, and over-tones which belong
to more than one single clang, are underlined. The difference-

1 When harmonious tones are simultaneously sounded, we have formed
not only difference-tones, but a second kind of resultant tonal wave, depend-
ing upon the fact that the hills and valleys of the primary waves are not
perfectly coincident. The vibration-rate of these new tone-waves is the sum
of the vibration- rates of the original tones. The tones themselves are,
therefore, of higher pitch than the principal tones in the chord, and are
termed, from their mode of origin, summation-tonts. Thus the fifth, 2 : 3,
has a summation-tone of the vibration-rate 2 + 3 = 5. Difference- and
•summation-tones together are sometimes called combination-tones. However,
the interpretation of the summation-tones is not beyond doubt, many
psychologists regarding them as high over-tones of the principal clangs. In
any event, they are so weak as to exert no influence upon the clang-character
•of the chord unless they coincide with over-tones. We may, therefore,
•leave them here out of account.

Noises 77-

tones which the over-tones form with one another, or with the
principal tones, are not set down. In most cases they are so-
weak as to be sensed with difficulty, or not at all. You see
that, even in a completely harmonious chord, the over-tones of
the second octave stand so near together as to produce very
considerable dissonance. Indeed, the most perfectly attuned
chords of an instrument whose clangs are rich in over-tones
(organ, harmonium) allow the beats of these over-tones to be
clearly perceived. They combine with the quality of the under
and over-tones to determine the general character of the-
different chords.

§ IV

The compound clang arises irom the single clang by the-
strengthening of secondary tones to principal tones. The
compound clang in its turn may pass over into the third
general sound-quality, into noise, as soon as the dissonant
elements, which we have found to be not altogether absent even,
in harmonious chords, multiply to such an extent that har-
monious tonal ratios cannot be any longer perceived. You
may easily convince yourselves of the origin of noise from the
compound clang by striking simultaneously upon some instru-
ment of wide range, such as piano or harmonium, a large
number of inharmonious tones. The separate tones make such
strong beats with one another that the resultant sensation tends,
to lose its clang-character altogether.

But when we seek to determine the point at which the clang
ends and the noise begins, we find that there is no sharp line of
division discoverable. In most noises we can distinguish one
or more deep tones, but these are accompanied by a crowd of
indistinguishable secondary tones, strong or weak, and of the
most different pitch. That is, the difference between clang and
noise is only one of degree. Noise and clang alike depend
upon the simultaneity of several tone-sensations. Even in the
clang, it is impossible to distinguish and identify the greater
part of these tone-sensations ; they merely serve to colour the
principal tone in a particular way, and it requires a sensitive ear
and close attention, or special experimental aids, to refer the
effect to its true cause. And the fact that the clang-colour

7 8 Lectures on Human and Animal Psychology

depends upon the occurrence of over-tones is further obscured
by the presence of the principal tone itself. With noise the
conditions are directly contrary : it is the mixture of tones
which plays the principal part, and the separate tone, in conse-
quence, tends entirely to disappear.

It is, however, probable that this, though the customary, is
not the only, mode of origin of noise. There is another, which
sometimes co-operates with the first, sometimes appears alone.
A vibration-rate the rapidity of which is high enough to
transcend the upper limit of tonal sensation is perceived as a
hissing noise, while very slow vibration-rates, which do not
reach the lower limit of tone, give rise to a roaring noise. It i-^
supposed that these sensations are caused not by the excitation
of the cochlear apparatus which is attuned to tone, but by the
vibrations of more simple organs, connected with the fibres of
the auditory nerve, and situated in the vestibule of the labyrinth
of the ear. Since the vestibule belongs to a much earlier stage
of development than the cochlea, we might interpret these
simple, absolutely toneless sensations as more primitive than
clang-sensations, and as constituting the whole series of sound-
sensation for most of the lower animals. When once the tone-
sensation has been developed, however, these toneless sensations
are completely overshadowed, even in perceptions of noise, by
the dissonant clang-constituents which enter, as we have seen,
into the maiority of noises.

§V

If we abstract from these elementary noise-sensations, which
are probably of high importance for the development of auditory
sensation in the animal kingdom, but which play so small a
part when once audition has been perfected, we may say that
all kinds of auditory sensation, — clangs, compound clangs, and
noises, — are combinations of simple tone-sensations. The
simple tone-sensation itself, however, cannot be analysed into
still more simple constituents : like every simple sensation, it
possesses only the two attributes of intensity and quality, i.e.,
intensity and pitch. Pitch, like intensity, can vary only in two
opposite directions, up and down ; we can pass from a given

Measurement of 7^onal Differences 79

tone either to a higher or to a lower one, just as from any
given point on a straight line we can proceed only in two
directions and keep within the line. That is to say, our whole
system of tone-sensations may be considered as a plurality in
one dimension, or as a linear plurality.

The analogy between the quality of tone-sensations and the
intensity of any particular pitch holds in yet another connection.
Intensity varies step for step with variations in the strength of
the external stimulus. In the same way, tone-quality follows
step for step variations in vibration- rate ; and we are as little
able to appreciate any the least alteration in vibration-rate as a
change in sensation-quality as we are to notice minute altera-
tions in strength of stimulus as changes of sensation-intensity.
In both cases there is a lower limit of discrimination. It is, of
course, not possible to determine this limit on ordinary musical
instruments with fixed note-values, like the piano, because the
tones are separated by far more than just noticeable intervals.
But if we take two similarly tuned strings or tuning-forks and
gradually alter the pitch of one of them, we have no difficulty
in discovering the point at which one tone sounds just notice-
ably deeper than the other. It is necessary, in making this
experiment, to strike the strings or forks successively, and to
check the vibrations of one before the other is sounded, since
otherwise beats would be produced, and the qualitative differ-
ence of the tones known from them, and not from the differences
in sensation. On the other hand, when the point at which a
sensation-difference becomes noticeable is once found, we may
employ the beats produced by the simultaneous sounding of
the tones to tell us the objective difference of vibration-rate,
corresponding to the bare possibility of their qualitative dis-
crimination in sensation. The number of beats, you will
remember, corresponds exactly to the difference between the
vibration-rates of the two sounding bodies. For instance, if
two similar tuning-forks have been so far removed from unison,
in the manner described above, that their successive tones are
just distinguishable as different pitches, and if we find that they
produce two beats in 10" when struck simultaneously, we may
conclude that at their particular pitch the just noticeable
sensation-difference is represented by a difference of o-2 vibra-

8o Lectures on Human and Animal Psychology

tion in i". Careful experimentation on these lines has shown
that the differences of pitch, which are just noticeable for succes-
sive stimuli, remain absolutely constant over a large part of the
musical scale. Between the limits of 200 and 1,000 vibrations
in the i", we can sense a tone-difference represented by O'2
vibration. For lower tones the fraction is somewhat smaller,
for higher tones correspondingly larger ; but within the sphere
of musical applicability there is no considerable deviation from
this average value. Where the tones are high or low enough
to approach the limit of sensibility, discrimination becomes, as
we should expect, far less certain. You may convince your-
selves of this by striking successive notes at either end of the
key- board of a piano : differences of a whole half-tone are
hardly perceptible.

Let us apply the general conclusions which we arrived at in
considering the question of the measurement of sensation-inten-
sity to this particular case. The result of our observations may
be summed up in a single sentence. Within wide limits, we have
found, equal differences of tonal quality correspond to equal differ-
ences of vibration-rate ; in other words, the sensation of pitch
varies in direct proportion to the objective variation of tonal
vibration. And there is another path which will lead us to the
same point. We possess an especial capacity for the quantita-
tive comparison of more than just noticeable differences of tone-
sensation. Suppose that we strike first the two tones c and d in
succession, and then the d and a of the same octave. Even the
most unmusical person, who has no notion of the intervals be-
tween the tones in the technical sense, is perfectly certain that
a and d are further apart than c and d. Here, then, is another
experimental method. Two tones at any distance from one
another on the musical scale may be given in succession, and
the observer required to estimate their exact sensation-mean,
the pitch which is just as far removed from the first as it is from
the second. It has been found that the tone selected as the
mean is always approximately the tone whose vibration-rate
lies midway between the vibration-rates of the two extremes.

But there are facts, recurring in the musical experience of all
times, which stand in apparent contradiction to these experi-
mental observations. These facts are expressed in the tonal

Tonal Scale 81

relations of the musical scale. We have seen that the vibration-
rate of the octave is invariably twice that of the ground-tone,
that of the fifth 3/2 of it, that of the major third 5/4, and so on.
The octave of the tone of 32 vibrations in i" makes 64 ; the
octave of this, 128, etc. That is to say, the higher the pitch, the
greater becomes the difference between the vibration-rates con-
stituting any particular interval. Nevertheless, the sensation-
difference between a tone and its octave appears to remain the
same from whatever region of the scale the interval is taken : the
difference in pitch seems unchanged whether we compare the tone
of 32 vibrations with that of 64, or the tone of 64 with that of 128.

The law regulating musical intervals, therefore, lays it down
not that pitch varies in direct proportion to variation of stimulus,
but that it varies more slowly than stimulus. And this law of
slower variation is, again, a very simple one. To increase tonal
qualities by equal increments, we must increase the rapidity of
their vibration- rates by a magnitude which always bears the
same relation to the rate to which it is added. To obtain the
octave of a given tone, its vibration-rate must always be multi-
plied by two ; to obtain the fifth, third, and fourth, its original
rate multiplied respectively by 3/2, 5/4, 4/3. And this result is
precisely parallel to that which we obtained when we were dis-
cussing the pressure of weights, the strength of sound and light,
in short, the intensity of sensation in general. In all depart-
ments of quantitative comparison we found that for the sensa-
tion to increase by absolutely equal magnitudes the external
stimulus must be increased by relatively equal magnitudes. We
have, then, only to write 'tonal quality' for 'sensation-inten-
sity,' and we have our law, — the same law which held for the
general relation of stimulus and sensation in the sphere of in-
tensity. If pitch is to increase by absolutely equal magnitudes,
vibration-rate must be increased by relatively equal magnitudes ;
or, more briefly,/z/<:/z increases in direct proportion to the logarithm
of vibration-rate.

Here, then, we are met by a very curious contradiction.
According to the law which regulates the musical scale, the
sensation of pitch is dependent upon stimulus in just the same
way as sensation-intensity is dependent upon it. But so soon as
we apply the methods which we used to measure intensity to

G

82 Lectures on Human and Animal Psychology

the measurement of quality in this particular case, we find,
within certain limits, a direct proportionality between variation
of sensation and alteration of vibration-rate.

The contradiction is only apparent. The most obvious way
to remove it, perhaps, would be to point out that sensation-
intensity and tone-pitch are different things. If Weber's law is
proved to hold of one of them, there is not the least reason to
assume that it will hold of the other. How were the musical
intervals established in the first place ? Not, at any rate, with
conscious reference to the fact that the same interval presents
the same difference for sensation from whatever region of the
tone-scale it is taken. We must look for other conditions, con-
ditions of our tonal sensibility in general, which give a definite
character to each tone-interval, quite apart from its position upon
the whole musical scale. They are not far to seek ; think of the
over-tones which accompany every simple clang. When a pitch
changes by the amount of some particular musical interval, the
character given to the clang by its over-tones must change in
the same way. Suppose that the change is that of a fifth. The
vibration-rates of the principal tones bear the ratio 2 : 3. The
clang-character of the lower one is determined by the over-tone
series : 4, 6, 8, IO, 12 . . . ; that of the higher by the series : 6, 9,
12, 15. . . . The relations of these two series remain the same
whatever the absolute pitch of the principal tones may be.

At the same time, the explanation is not satisfactory. Granted
that this constancy of the relations of the secondary tones in
every interval gives a reason for the dependency of the musical
intervals upon constant relations of their constituent vibration-
rates, still the problem is only pushed one step farther back, not
solved. If we are to know that an interval is the same when it
is given, say, first in the upper and then in the lower region of
the scale, we must apprehend in sensation the likeness of the
interrelations of all the partial tones in the two cases. But what
is true of secondary tones will be true of their primaries. As a
matter of fact, we are able to cognise the harmonic intervals of
pure tones, which are practically free from over-tones, with
almost as much accuracy and certainty as the intervals of clangs
whose over-tones are numerous and intensive. That is to say,
though our apprehension of harmonic intervals may be furthered

Weber 's Law and Tones 83

by the compound character of the single clang, there must be
operative some more ultimate influence than this, which we have
not yet found. To which must be added that the contradiction
resulting from the application of the customary methods of sen-
sation-measurement to the intensity of sensation on the one
hand, and to the pitch of tones on the other, is not in the least
degree removed by the adoption of the proposed explanation.
The answer that intensity and quality are two different things
simply gives up any attempt at an adequate explanation of the
incongruity of the two sets of results. As a matter of fact, there
is a complete parallelism between the continuous gradations of
stimulus-intensity and vibration-rate, of sensation-intensity and
tonal pitch.

But there is one way of escape still open to us. Recall to
mind the psychological interpretation which we offered of
Weber's law. We explained the law by assuming that in esti-
mating differences of sensation it is the relative, and not the
absolute magnitude of the compared sensations which we re-
gard. But there is always the possibility of an absolute estima-
tion by the side of this relative one. And we shall expect to
find the possibility realised in all cases where a sensation, for
some reason or another, is apprehended by itself, in isolation from
the remaining terms of the sensation-series to which it belongs.
That, again, will occur, and only occur, when the effect of the
sensations upon consciousness is not such as to necessitate a
reference to other sensations of the same kind. Now this refer-
ence is inevitable in every apprehension of an intensity. A loud
sound makes greater demands upon consciousness, so to speak,
than a weak one. For a sensation-increment to possess the same
magnitude in the two cases, therefore, the increase of the
stronger stimulus must be greater in proportion as the stimulus
itself and, consequently, its effect upon consciousness is greater.
But with tone-pitch the case is quite different. A high and a
low tone may well be upon a perfect equality as regards the in-
tensity of their effect upon consciousness. That is, the criterion
of our discrimination of two tones whose qualitative difference is
just noticeable can only be their absolute difference in sensation,
which is paralleled by the absolute difference between their
vibration-rates. And a comparison of this kind will be possible

84 Lectures on H2iman and Animal Psychology

for tones whose difference is more than just noticeable ; so that
in subdividing such a total difference into two equal smaller
differences we shall always have in mind an absolute, and not a
relative, standard of measurement. It is, of course, still another
case, if we propose to find two tones at one part of the scale, the
relation of whose qualities is similar to that of the qualities of
two given tones from another part. In this case the difference
is stated in the formulation of the problem to be a relative one \
and the interval is chosen with a view to this relativity. Coinci-
dence of over-tones will certainly help us in this case to cognise
the likeness of the two intervals compared ; all that we insist on
is, that it is not the sole determinant of our estimation. It is
true that the repetition of the fifth, eg; in a higher octave
allows of a readier cognition of the particular interval than the
giving of the tones da or fc. But, nevertheless, the likeness
of these two intervals to the first does not remain doubtful for
a single moment.

Our views as to the significance of Weber's law are, then,
partly confirmed and partly supplemented by the facts which
we have learned as to our apprehension of differences of
tonal quality and of tone-intervals. Partly confirmed : for we
have found still further reason for our supposition that Weber's
law is to be interpreted as a law of the relative estimation of sen-
sation-magnitude. Tone-intervals furnish us with particularly
convincing evidence of the truth of this law of relativity. Partly
supplemented ; for we have found that where the conditions of
our apprehension of different sensations suggest an absolute
rather than a relative comparison, a simple proportionality takes
the place of the logarithmic relation between stimulus and
sensation. This fact serves at the same time to disprove once
and for all the psychophysical theory of Weber's law, which
saw in it an expression of the universally valid relations obtain-
ing between the psychical and the physical. Such a hypothesis
could only be maintained, if the sensation itself, apart from the
psychological processes involved in its comparative apprehen-
sion, were subject to the logarithmic law. • Nor is the physio-
logical theory, — that is, in its customary form, — less clearly dis-
proved. It supposes that the conduction of the sense-excitation
in the brain meets with obstacles, which increase as the magni-

Weber 's Law and Tones 85

tude of the stimulus increases, so that the excitation in the
central organ itself increases more slowly than the external
sense-stimulus, the exact amount of its inhibition being ex-
pressed in the logarithmic formula. The fact that, under con-
ditions which exclude the influence of comparison in estimation,
the course of sensation and stimulus is within limits a perfectly
parallel one, makes against this supposition. It must rather be
the case that within these limits there is a direct proportion-
ality between central and peripheral excitation. So that if we
are led by the principle of psychophysical parallelism to look
for a physiological basis, as well as for a psychological explana-
tion of Weber's law, our field of search must be the relations of
the stimulation-processes in some sensory centre of a higher
order, where are aroused the physical excitations which underlie
a relative apprehension of sensations.

Our general conclusion, therefore, will be this : wherever we
are able to bring about a continuous alteration in the intensity
or quality of stimulus and sensation, we shall find certain limits
within which the alteration of sensation runs directly parallel to
the alteration of stimulus. On the other hand, when we are
comparing different sensations with one another, we shall expect
to find our estimation of their magnitude determined as absolute
or relative by the special conditions of the investigation. A
just noticeable difference in the intensity of sensation is always
apprehended in relative terms ; for the amount of increase which
is equally noticeable in different cases depends upon the de-
mands made upon consciousness by the particular sensation.
The greater the intensity of the sensation, of course, the greater
its effect in and upon consciousness. Our estimation of tone-
intervals is also relative : it is the relation of the terms, not
their absolute value, upon which we have to direct our attention.
Nevertheless, it is not difficult to perceive that the same interval
represents a greater absolute sensation-difference in the upper
region of the tonal scale than in the lower, unless the tones
which compose it are so very low or high that our discrimination
fails us. If we strike first the tone c followed by g, and then
g followed by d', — if we give, i.e., two opposed fifths in succes-
sion, and concentrate the attention exclusively upon the absolute
sensation-difference, — we have no hesitation in declaring the

86 Lectures on Human and Animal Psychology

• distance^' to be greater than eg. And this helps to explain
the converse fact : that when we are halving more than notice-
able tonal differences simply in terms of their absolute value in
sensation, and without regard to them as musical or unmusical
intervals, or when we are determining just noticeable differ-
ences of tonal quality, we estimate absolutely, and not relatively.
So that if we are to sum up the result of this whole discussion
in one general proposition, that will run somewhat as follows : —
Unless a sensation approaches the upper or lower limit of sensi-
bility, alteration in it is directly proportional to the absolute magni-
tude of alteration of its stimulus. But our apprehension of
alteration in sensation remains only relative so long as its absolute
perception is not made possible by the express introduction of
especial conditions.

LECTURE VI

§ I. LIGHT-SENSATIONS ; SENSATIONS OF COLOUR AND BRIGHTNESS ;

ANALYSIS AND MIXTURE OF COLOURS. § II. THE THREE PRIMARY

COLOURS. § III. LEONARDO'S FOUR PRINCIPAL COLOURS. § IV.
THEORY OF LIGHT-SENSATIONS.

§1

VISUAL sensations have two qualities, — colour and bright-
ness. The latter term includes black, white, and all the
various shades of grey. The number of distinguishable colours
is enormous : it has never been determined. But it is a fact
of immediate perception that the variety of colour in nature is
not altogether heterogeneous : there are very many intermediate
tints between this colour and that. And if we try to divide up
the whole multifarious colour field, and to separate out the colours
which are clearly and definitely unlike the rest, we can reduce the
list of ' pure ' colours to very small dimensions. Red, yellow,
green, blue, together with black and white, prove to be the
simple and ultimate qualities which we are able, so to say, to
abstract from the innumerable specifically different presenta-
tions of nature. All other distinguishable colour-tones are
intermediates, — a fact which is very frequently expressed in the
names given to them (purplish red, orange-yellow, yellowish
green, violet-blue, etc.). But these six simple qualities, again,
are not co-ordinates ; they evince different degrees of variety or
resemblance. We are inclined to regard green as being nearer
blue than yellow is, and to look on red and yellow as pretty
closely related colours, even when the intermediates blue-green
and orange are not present to suggest the comparison. It might
be thought that this notion of colour relationship was due to our
knowledge of colour sequence in the rainbow. But children
who have never observed a rainbow with any degree of attention
will usually connect blue with green, and red with yellow, when
required to arrange the four qualities in the order of likeness.

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$8 Lectures on Hitman and Animal Psychology

The hypothesis that there is a limited number of simple
colours, from which we may conceive all the other qualities of
light to be compounded, is thus suggested by the subjective
relationship obtaining between certain colour-tones. It is fur-
ther confirmed by the familiar results of the mixture of pig-
ments. The painter has long known that green can be obtained
by mixing yellow and blue, violet and purple by mixing blue
and red. It was an obvious corollary that every colour which
could be produced in this way by the intermixture of other
colours was in itself a complex, not a simple, sensation-quality.
No distinction was drawn, you see, between objective light and
subjective light-sensation ; if the external light is a complex, it
was thought, the sensation corresponding to it must be a complex
also. And even to-day the painter is wont to look upon red,
blue, and yellow, together with black and white, as the simple
qualities by whose intermixture all other colours are produced.

The science of colour went still farther. Colours usually differ
not only in tone, but in brightness ; red appears darker than
yellow, etc. So it was thought possible to arrange all the colours
in a series, the terminal members of which should be constituted
by the two extremes of brightness, — black and white. Aristotle,
for instance, taught that black and white are the two fundamental
qualities of light, and that every colour can be obtained from
their intermixture in varying amounts.

From the point of view of direct perception, the simplicity
and universality of this hypothesis are very tempting. When
we have once convinced ourselves that the great majority of
colours in nature result from the intermixture of a small number
of simple qualities, and that these themselves are sensibly related
to one another, our mind will not be at rest till it has reduced all
the phenomena to two polar opposites. And these can be nothing
else than black and white. For all the true colours stand some-
where between these two in brightness, approaching white if
their brightness is increased and tending towards black if it
is diminished. If all colour is to be derived from two opposites,
those opposites must be black and white.

The Aristotelian view of the origin of colour prevailed, then,
until modern times. Goethe defended it, and many of his
admirers are its enthusiastic champions. But it has been ban-

Light-sensations 89

ished from science these two hundred years, thanks to Newton's
discoveries. Newton said to himself : If there really are simple
kinds of light or simple colours, which intermix in various ways,
we must be able both to isolate and to recombine the simple
constituents of any given compound colour. That meant that
the whole question was referred to the tribunal of experiment,
where alone it could be definitely answered. For direct percep-
tion is deceptive. Can the chemist ' see ' of what elements a body
is composed ? Of course not. We know that bodies of very
different chemical composition appear just alike. May not the
same hold of light ? May not similar kinds of light give rise to
different mixtures, and different kinds to similar mixtures ? So
Newton looked round him for a means of analysing compound
light, and by a happy accident found what he wanted in the
refraction of light by the prism.

If we allow a ray
•of light coming from
a to pass through a
prism, /, of glass or
some other trans-
parent substance, its
course is not the
straight line that it

would be if no prism

FIG. 8.
were in its way, but

it is turned aside, refracted, as we say : so that an eye, o, behind
the prism receives it as if coming from b or thereabouts ; the
source of light is transposed from a to b. Moreover, the point
from which the ray appears to come in the direction bd does not
always remain the same. It varies with the quality of the light.
If, e.g., a is light of a blue colour, and the ray is seen as though
it came from b, a red a will emit a ray which appears to travel in
the direction re, r lying higher than b and nearer to a. It follows
that different kinds of light are not refracted in the same degree
by the same prism and under similar experimental conditions,
Red light is less strongly refracted than blue ; r is nearer a than
b is. On comparing the different colours with one another, we
find that they fall into a definite series in regard to refrangibility.
Red is least, violet most, refracted ; and the series runs — red,

90 Lectures on Human and Animal Psychology

yellow, green, blue, violet. Tones interpolated between two*
neighbouring colours possess an intermediate degree of refrangi-
bility. Orange lies between red and yellow, greenish yellow
between yellow and green, indigo-blue between blue and violet.

How is it with regard to white ? White is, of course, the
most widely diffused quality of light ; it is that of sunlight. It is
the light which we ordinarily see, if its character is not modified by
the peculiar colour of an object. A ray of white light sent through
a prism is affected in this way : the eye that receives it after its
passage finds it not white at all, but distributed into a whole
number of colours ; so that if a is a point of white light, the ray
proceeding from it is not refracted simply like a ray of mono-
chromatic light, and its source transposed from a to r or b, but
it seems to issue from a series of sources arranged in a vertical
line, each showing a different colour. Violet stands at the
bottom ; and then follow blue, green, yellow, and red. White
sunlight is, therefore, not simple, but capable of analysis into a
large number of simpler light-qualities. These, on the other
hand, are not further decomposable. However often we pass
pure red or pure yellow through a prism, it retains its character
unaltered. You notice that the colour-series obtained by the
refraction of white sunlight, whether experimentally or naturally
— the rainbow is caused by refraction in the particles of water
suspended in the atmosphere, — contains all the colours which
occur in nature. By mixing its tones in the right proportions,
we can produce any colour that we wish. This is really self-
evident, since all the light that the earth receives is derived
from the sun. So that, whether a natural body reflects or
absorbs light, no effect can arise whose cause is not contained
in the constitution of sunlight. As the intensity of white light
decreases, we gradually arrive at darkness, or black. Black,
that is, is not a colour, but the minimal degree of brightness of
white light.

The facts obtained by this exact analysis of light were, how-
ever, difficult to reconcile with the results of the mixture of
colours, which had also been reached by way of observation.
The spectrum produced by the analysis of white sunlight has,
you see, at least five colours, — and still more if we count in the
intermediate tints. But painters had long since noticed that

Light-sensations 9 1

all possible varieties of colour could be produced from three
simple tones. It is true that the resulting mixtures are not so
saturated as the spectral colours ; but still they are as saturated
as most of the colours occurring in nature. The three colours, —
primary colours, they were called, — which could be so inter-
mixed as to give rise to any other colour-variety, were generally
given, as we have said above, as red, yellow, and blue. But it
is better to take red, green, and violet ; and it is better, instead
of mixing pigments, to mix directly colours that have been
separated out from sunlight by the prism, or to allow colour-
impressions to follow one another so quickly that they fuse for
sensation. The colours to be mixed can be painted upon
the sectors of a round disc, and the disc rapidly rotated on a
top or by clock-work. This gives us a perfectly uniform im-
pression. Red, green, and violet employed in
their right amounts produce white ; and every
distinguishable colour-tone corresponds to
some particular mixture of the three funda-
mental colours with one another and with
white. White can also be obtained by the
mixture of two colours situated at the right
distance from each other in the spectral series. FlG- 9-

The constituents of such pairs as, taken together, give rise to-
white, are called complementary colours. Green-blue, e.g., is
complementary to red, blue to orange, indigo-blue to yellow.
Green is the only pure spectral colour that has no comple-
mentary. To produce white it must be mixed with purplish,
red, a combination of red and violet. That, of course, is
equivalent to a mixture of the three primary colours.

How is this contradiction between the analysis and syn-
thesis of light to be got over? It is generally left unchallenged,
as it was by Newton himself. He said : There are combined in
white light particles of red, yellow, green, blue, and violet light,
and the prism isolates each separate ray ; but when we are:
putting together particles of different kinds of light, three of
them, — red, yellow, and blue, — are enough to produce all the
phenomena. Analysis, you see, had come into conflict with
synthesis ; and physical science was not sufficiently advanced to-
set them at one again.

'92 Lectures on Human and Animal Psychology

The first step towards reconciliation was taken when it was
discovered that Newton's theory of light was incorrect. He
held that the particles of light were themselves coloured, and
that light was a substance continually emitted by the sun, and
containing in it a multitude of particles of the most diverse
colours. This view had often had objections urged against it ;
but it was reserved for the French physicist Fresnel to adduce
a direct disproof of it by experiment. Fresnel showed that
when light meets light it is by no manner of means necessary
that an increase of intensity should result. Were light a sub-
stance, that must be the case. But, as a matter of fact, decrease
of intensity is as common a phenomenon as increase. These
observations of what is known as the ' interference ' of rays of
light prove indisputably that light is not a substance, but a
-movement. Two intercrossing movements may result either in
an increase or decrease of intensity : nothing else can. If two
balls travelling in opposite directions with equal force meet
-each other, their movement is annihilated ; if they are travelling
in the same direction, it is accelerated. If two waves of water
meet, there is increase of the wave where crest and crest come
together, decrease or annihilation where crest meets valley.
The phenomena of interference show that there are wave-crests
and wave-valleys concerned when rays of light meet one
another ; that light-intensities will increase at one point of
junction, while they decrease at another ; in other words, that
we have to regard light as a movement analogous to the move-
ment of a wave in water. If you throw a stone into water, you
start a wave, which extends in every direction. The shock of
the stone gives rise to a vibration which is transmitted from one
particle of the liquid to another. Light consists of vibrations
of this kind, except that the substance in which they are set
up is infinitely less dense than water. It is a form of matter
which interpenetrates all physical bodies, solids and liquids
as well as gases, besides filling the space between them. The
particles of this ' luminous ether ' are set in vibration in the
fiery atmosphere of the sun, and the movement is transmitted
from particle to particle at the enormous velocity of 186,000
miles in the second. What our eye senses as an impression of
•light, therefore, is not a substance penetrating to it from the

Light- sensations 93

remote depths of space, but a movement which, to excite our
sense-organ, must be continuous through all the vast distance-
which separates us from its place of origin. It is one and the
same form of matter which occasions all the multifarious sensa-
tions of light and colour ; so that difference in sensation can
only mean difference in the movement of the luminous ether.
Accurate measurements of the effects of interference have en-
abled the physicist to determine this difference in different cases,
and it has been found that colour-differences depend upon
differences in the velocity of the oscillations of the particles of
the luminous ether. In red light, the number of oscillations is-
something between 400 and 500 billions in l" ; in violet, it ap-
proaches 800 billions. All the other colours lie between these
extremes. Orange has 500, green 600, blue 650, and indigo-
blue 700 billions in l" ; so that the spectral colours constitute
a progressive series within whose limits the velocity of vibration
increases by nearly 400 billions. It is worth noticing that sun-
light contains, besides these coloured rays, other vibrations
which are invisible, not sensed as light. There are rays less-
strongly refracted than the red, and rays more strongly refracted
than the violet ; vibration-rates, i.e., both greater and less than
those which the eye senses as light or colour. The invisible rays
beyond the red end of the spectrum manifest themselves as heat ;
those beyond the violet, in certain forms of chemical action.

It is, you see, only a comparatively narrow section of the
ether-vibrations which has the power of exciting a retinal sensa-
tion. The whole variety of colour-tone is included within
these narrow limits, and a very slight change in vibration-rate
suffices to produce a noticeable difference of colour-sensation.

These brief remarks upon the physical nature of light will
serve to show you that light and colour have no objective reality,
— i.e., do not exist as light and colour outside of and around
us, — but that all the properties by which we discriminate light as
such, and the various separate colours from one another, are
within us, originating in our colour- and light-sensations. What
we call light and colour is just our own sensation of light and
colour. Outside of us there is no system of sensations, but only
vibrations in the ether. And the proof that light and colour
are subjective phenomena marks an important step in psycho-

94 Lectures on Human and Animal Psychology

logical as well as in physical knowledge. We now know that
a complete explanation of the phenomena of light and colour
cannot be based solely on a physical examination of light, but
must also take account of the conditions under which we sense
it. What we sense, once more, is not the ether-vibration, but
the particular reaction of our eye and mind upon that vibration.
Movements which are too fast or too slow to be perceived by
the eye are evidently removed from the list of visual stimuli
simply by reason of their velocity. But objectively they may
be light, just as much as any other movements.

So that, if we are attempting an explanation of the phenomena
of light and colour, the result even of a purely physical investi-
gation will be to refer us to the seeing subject Now you
remember that we had come across a contradiction. The
analysis of light by the prism told us one thing ; the recompo-
sition of the various light-qualities told us another. We can
separate out from sunlight at least five simple colours, without
counting intermediate tints, while we can produce every colour
that occurs in nature by the intermixture in appropriate amounts
of three colours only, best chosen as red, green, and violet.
How is the contradiction to be met ?

It is evident from what has been said above that the fact that
white and all possible colours can be obtained from three
primary colours does not mean that objective light is com-
pounded of those three fundamental colours. Nor does it
mean, as many physiologists would still have us believe it does,
that all our subjective light-sensations are derived from three
ultimate sensations corresponding to the three primary colours.
All that the results of experiments upon colour-mixture
prove is this : that three objectively simple modes of vibration
are sufficient, when mixed in different amounts, to set up all
those stimulation-processes in the organ of vision which can
be occasioned by the colours of the solar spectrum and their
intermixtures.

The three primary colours could only possess any sig-
nificance in physics if objective light were analysable into
three modes of vibration, corresponding to them, and no more.
We have seen that that is not the case. In one way the
primary colours do occupy exceptional positions in the infinite

Light-sensations 95

gradation of light-vibrations. Red and violet stand at either
-end of the series of visible vibration-rates, and green is situated
at its centre. But this, though a fact of some importance for an
examination of the conditions under which the eye is stimulable
by light, has no reference whatever to objective light as such,
the light whose vibration-rates extend far beyond the limits
within which the ether rays are visible.

The primary colours would only possess significance in
psychology if we could subjectively, in immediate sensation,
analyse all our light-sensations into these three particular con-
stituents. We can, certainly, say that orange is a sort of mix-
ture of red and yellow, violet a mixture of blue and red, and so
on. But even in these cases the phrase ' intermediate between '
would be more correct than ' mixture of.' It seems to me, at
any rate, that my sensation of orange and violet makes of them
impressions as simple as it does of red, blue, or yellow. And so
much is indisputable : that no one can say he senses red and
green in yellow, or red, green, and violet in white. Subjectively
white is just as simple as any simple colour. And black we
shall all incline to regard not only as the minimal degree of
intensity of white, but at the same time as its qualitative
opposite.

There is only one possibility left If the existence of three
primary colours is incapable either of physical or of psycho-
logical explanation, it must depend simply and solely upon
physiological conditions. If we accept the principle that to every
difference in our subjective sensations there corresponds a differ-
ence in the physiological stimulation-processes within the sense-
organ, we must suppose that the three objective light-qualities
in the red, green, and violet portions of the spectrum, when
mixed in the right proportions, can set up as many physiological
excitatory processes as there are subjectively discriminable
sensations. How many of these stimulation-processes are
possible we cannot directly determine : but they must be esti-
mated from the number of distinguishable sensations, and not
from the number of objective light-stimuli by which the sensa-
tions are occasioned.

96

§ II

Simple as these considerations are, they have not as yet beet*
able to command anything like universal assent. In the current
theories of the nature of light and colour-sensation we find all.
too often a confusion between the physical and the physiological
stimulus, and again between this latter and the sensation
correlated with it ; or, if not that, the opposite error of a deriva-
tion of the objective conditions of light-excitation from the
subjective differences in sensation, — a hypothesis arbitrary in-
form and contradictory of experience in content.

For instance, Thomas Young, an English physician and
physicist of the beginning of the present century, maintained
that all our sensations of light and colour are compounded of
the primary sensations red, green, and violet. There exist in-
the eye, he said, three kinds of nerve-fibres, sensitive respectively

Grun

Gelb

Blau

Roth

Orange

Indigo

VMett

to the red, green, and
violet rays. We can-
represent the laws of
colour - mixture by
drawing a triangle, as
in Fig. 10, the three
angles of which are
constituted by the
three primary colours,
while the intermediate
spectral tints are placed
along its sides, — purple,

furpur
FIG. 10.

e.g., between the red and violet of which it is compounded, — and
white occupies the centre of its area. Such a triangle, accord-
ing to Young, would express equally well the conditions of
visual sensation and visual stimulation. Orange and yellow, for
example, would excite the fibres sensitive to red and green, the
red predominating in orange, and the green in yellow, while the
sensation of white would result from the excitation of all three
fibres in approximately equal intensity. The sensation of
white, that is, is simply a mixture of the three sensations red,
green, and violet. The impression of a whitish colour occurs,
on the other hand, if one or two of the primary colours

The Three Primary Colours 97

predominate in the mixture. These whitish colour-tones may
therefore be written in upon that portion of the area of the
triangle which lies between the centre (white) and the sides.

Thomas Young regarded his own assumption of three funda-
mental sensations as no more than a provisional hypothesis,
especially useful for the explanation of the phenomena of colour-
mixture. But many physiologists and physicists of recent times
have imagined this supposed structure of the organ of vision to
be a necessary corollary from the facts of colour-blindness, and
so have made the hypothesis a certainty. Colour-blindness does-
not, as a rule, signify blindness to colour in general, but only
insensibility to certain particular colours. If it is connate, the
colour-blind person need not be conscious of his defect, which
simply consists in the confusion of special colours, — red and
green, e.g., — clearly distinguishable by the normal eye. Experi-
ence shows that in the great majority of cases colour-blindness is
red-blindness, though green-blindness also occurs. But red and
green are fundamental colours, so that we seem to have in the
phenomena a confirmation of Young's theory. The condition
of the eye, you see, is quite easily explicable in terms of it We
have simply to regard one of the three sets of nerve-fibres or
terminal organs of the normal eye as absent or functionless : in
red-blindness those sensitive to the red rays ; in green-blindness
those sensitive to green.

Nevertheless, the proof is not so unexceptionable as has often
been thought. If we grant that the only forms of colour-blind-
ness are the ' red ' and ' green ' types, we may, perhaps, find it
to be a necessary inference that there are normally particular
portions of the retina especially sensitive to red and green light,
and that these, for some unknown reason, are in the defective
organ either absent or insensible ; but we shall not find the least
ground for supposing that the sensation of yellow, e.g., is a mix-
ture of the sensations of red and green, or that stimulation by
yellow light simply means a stimulation of the elements sensi-
tive to red and green. The first proposition is negatived by the
character of the sensation ; yellow is qualitatively different both
from red and green, and shows no trace of a mixture of the two.
The second we can hardly regard as probable, unless we are will-
ing entirely to give up the principle which has stood us in such

H

98 Lectiires on Human and Animal Psychology

good stead heretofore, — the principle of parallelism of differences
in physiological stimulation with differences in sensation. But,
besides this, the progress of our knowledge of the phenomena of
colour-blindness has brought facts to light which are irreconcil-
able with Young's hypothesis. First of all, it has been found
that ' red ' and ' green '-blindness, though the commonest, are
not the sole types of abnormal colour-sensibility. Cases are
known of insensibility or diminished sensibility to other rays in
the spectrum, especially the yellow and blue. Secondly, there
are extant observations of unilateral or monocular colour-blind-
ness. Now, on Young's hypothesis, white must here be com-
posed of different primary sensations in the two eyes ; in
unilateral red-blindness, e.g., it would be a mixture of red, green,
and violet in the normal eye, of green and violet only in the
other. The same white light would therefore be differently
sensed by the two eyes ; to the normal it would appear white,
to the other, which has no sensation of red, greenish. As a
matter of fact, this is not the case ; the same white appears
precisely the same to both eyes. Thirdly and lastly, we have
instances of total colour-blindness. This generally results from
disease of the eye, and is frequently confined to one retina, or
even to portions of it. Black and white, with all the inter-
mediate greys, can still be sensed, but there is no sign of a
colour-sensation of any kind. A picture looks like a drawing ;
light and shade are clearly distinguished, but there is absolutely
no perception of colour. It is obvious that such a state of
things could never come about if every light-sensation were the
resultant of a mixture of the three primary colours. Total
colour-blindness would be impossible unless the sensation of
brightness and that of colour were correlated with different, and
under certain circumstances separable, excitatory processes in
the visual organ. And here we have a fresh proof of the validity
of our principle that difference of physiological stimulation-
process runs parallel to difference in sensation. For this
independence of white from the various colours might have been
inferred before from the independence of its quality in sensation.

Leonardo s Four Principal Colours 99

§ HI

These facts have, of course, told against Young's theory ; and
an attempt has been made in quite recent times to replace it by
another. To this end the views of Leonardo da Vinci — a name
as conspicuous in the history of science as in that of art — have
been revived. Leonardo regarded four colours, which he called
principal colours, as of prime importance, and looked upon all the
others as intermediate or mixed colours. These principal colours
were red, yellow, green, and blue. To them must be added black
and white. From the six fundamental qualities so obtained and
from their intermixture in various amounts all our sensations of
light and colour could, he urged, be derived. Orange, e.g., is
given in immediate sensation as a mixture of red and yellow,
violet as a mixture of red and blue.

Leonardo's view is entirely based upon the subjective cha-
racter of our sensations. And it might perhaps have held its own,
being not without interest as an expression of the psychological
side of the matter, if the attempt had not been made to graft
further hypotheses upon it for the explanation of the objective
laws of light-stimulation and colour-mixture. But it was
assumed, e.g., that between the members of each pair of principal
colours there existed an ' antagonism ' analogous to that between
white and black. Antagonistic colours were defined as those
which cancelled each other when mixed, leaving only the sensa-
tion of brightness, which accompanies every colour-sensation of
whatever quality. Red and green, blue and yellow, were
regarded as antagonistic in this sense. To make the dominant
idea of the theory still more definite, it was supposed that there
are intermingled in the retina three' different kinds of sensitive
substance, in each of which two antagonistic processes may be
set up, corresponding in a manner to the processes of anabolism,
or assimilation, and catabolism, or dissimilation, which are found
together throughout organic nature.

For the sake of brevity, we will term these processes a and dy
and call the three substances, after the sensations which they
mediate, the black-white, the red-green, and the blue-yellow.
The assumption then is, that the sensation of black is due to an
^-process, white to a ^-process, in the black-white substance ; in

ioo Lectures on Human and Animal Psychology

the red-green, red is the a and green the ^-process, or vice versa ;
and similarly with the blue-yellow. But every stimulation of a
colour-substance involves the excitation of the black-white ; and
so it comes about that if the a and ^-processes of one or both
colour-substances cancel each other, we still sense brightness.

It cannot be denied that this theory has done good service.
For the first time since the banishment from science of the older
colour-theory of Aristotle and Goethe, it called attention to the
fact that white light is just as simple in sensation as any mono-
chromatic light, and that black and white are not only to be re-
garded as different intensities of a single quality, but also, and
indeed predominantly, as qualitative opposites. In all other
respects, however, it is simply an arbitrary combination of arbi-
trary assumptions. Even the analogy between the ' antagonis-
tic ' colours and the black-white pair cannot be carried through.
When we mix black and white we get grey. And grey is
directly sensed as a quality intermediate between the two ex-
tremes. But when we mix red and green or blue and yellow,
there is no mixture, but only mutual disturbance in sensation ;
the only thing that is left is white, and white was present from
the beginning, except that the colours were too strong for it.
Again, the primary colours, indicated by the laws of mixture,
have to be accommodated to Leonardo's principal colours. That
is not altogether easy. We are obliged to change the names of
the colours to suit our theory. For the antagonistic colours are
not what we generally call pure red and pure green, pure yellow
and pure blue ; if we are to obtain complementariness, the red
must be tinged with purple, and the blue with indigo-blue, — in
other words, both these principal colours be mixed with a con-
siderable amount of violet. And, lastly, it is a necessary conse-
quence of the theory that there should be no partial colour-
blindness without annihilation or diminution of the sensibility
to the two members of some pair of antagonistic colours. For
it can only explain the affection as the result of some defect in
one of the two colour-substances. We ought, that is, to find
red-green and blue-yellow blindness, but no other form. As a
matter of fact, there cannot be any doubt at all that red-blindness
may occur without green, and green without red-blindness.

But not only does the assumption of antagonistic colour pairs-

Leonardos Four Principal Colours 101

come at every point into conflict with facts : its psychological
foundation is exceedingly questionable. The four principal
colours, — red, yellow, green, and blue, — are, you see, the only simple
sensations ; all other colours are immediately given as compound
in sensation. What support is there for that assertion ? Plainly
this, first of all : that when we have once recognised these four
as fundamental sensations the others fall into place readily
enough as subjective intermediates ; and secondly this : that
the names of these four are by far the oldest colour-names, the
others bearing the evidence of modernity upon their face. Now
the first of these facts is only of importance in the light of the
second. If language had originally contained special names,
say, for orange and violet instead of for red and yellow, it is
quite probable that we should be inclined to look upon these
latter as intermediate tones. So that everything depends upon
the answer to be returned to the question : why is it that these
particular four ' principal ' colours were the first to receive definite
colour-names ?

From the point of view of the theory which is under considera-
tion, it is a matter of course that the reason can only be looked
for among the immediate facts of sensation ; that red and yellow
are just given as simple, while orange is sensed as a compound
impression. Language, that is, preferred at the outset only to
name what was simple in sensation. Now this view obviously
proceeds from a wrong postulate as regards the origin of word-
symbols in language. In the first place, it is not true that a
separate word must exist for every qualitatively simple sensation.
More than one philologist has called attention to the fact that
a sharply distinguished term for ' red ' appears earlier than one
for 'blue.' In the ancient literatures, — e.g., in Homer, — the
expressions for the blue of the sky are such as could be used for
any dark or grey object. Now and again the conclusion has
actually been drawn from this that the Greeks of Homer's time
had not yet sensed blue ; that is, that the colour-sense in man
has within this comparatively short period undergone a very
considerable development. We shall hardly feel tempted to
assent to that conclusion. Language does not distinguish every-
thing that sensation distinguishes ; it contents itself with creating
special terms for those impressions whose discrimination is

IO2 Lectures on Human and Animal Psychology

necessary for the expression of thought and its communication
to others. Are we to suppose that it is only since Newton's day
that mankind can distinguish orange from yellow, or indigo-blue
from sky-blue? Surely not. These new names of colour-tones
simply came into use when they were needed for optical or
technical purposes. To make assurance doubly sure, it has been
quite recently proved that the scale of colour-sensations in
various savage races presents no differences from our own.

At the same time the four principal colours do in one sense
constitute a special case. Whenever different colour-names
occur, they are ultimately reducible to these four. So that there
is some show of reason for assuming their original sensational
preference. Nevertheless the law holds even here that language
does not name sensations because of any subjective peculiarities
that they may possess, but merely with reference to their
objective significance. So that whenever we can follow a colour-
name back to its original meaning we find it indicating some
external object by which the colour-sensation is occasioned.
Orange, indigo-blue, and violet are named from the colour of the
fruit, the dye-stuff, and the flower. Now what are the colours
which mankind would have named first, on this principle ?
Surely either those which excited in them the strongest feelings,
or those which were commonest among the natural objects of
their environment : the red of blood, perhaps, the green of
vegetation, and the blue of the sky, against which the bare earth
and the light of sun, moon, and stars looked yellow instead of
white. So that there is no need for us, in our search for the
origin of the four principal colours, to descend into the bottom-
less abyss of theory, and postulate a sensation that is independent
of any impression. And, of course, these colour-impressions,
which frequent repetition or some other reason has brought
more prominently than the others before consciousness, must
obtain an advantage not only as regards linguistic expression,
but also in sensation itself, in that all other sensations are
arranged with reference to them. If once red and yellow are
given, orange can only be looked upon as an intermediate tint.
In the same way purple and violet fall into place between blue
and red. And since there is a continuous transition from colour
to colour, while the range of sensation is strictly limited, the four

Theory of Light- sensations 103

principal colours were amply sufficient to allow of a permanent
arrangement of all the possible colour grades. Had the dominant
impressions, which determined at once colour-arrangement and
colour nomenclature, been orange, yellowish green, greenish blue,
and violet, instead of red, yellow, green, and blue, we should
undoubtedly have sensed red as an intermediate between violet
and orange, and green as a tint lying between yellowish green
and greenish blue. Isolate any one of these colours for your-
selves from the spectrum, and ask yourselves whether the
impression it makes is not that of absolute simplicity, if once
you abstract from the relations into which it has been brought
with other colours by the customary arrangement of the colour-
system.

§ IV

The principal colours owe their prominence, then, not to any-
thing in the quality of sensation itself, but to external circum-
stances which have nothing at all to do with sensation-quality.
Subjectively every colour-impression is a simple quality,
resembling its nearest neighbours, but only resembling them
because of the continuity of tints in the colour series. And the
mention of this fact of continuity leads us to another point,
which the two colour theories discussed above leave entirely out
of account, — the relation of the two terminal colours of the
spectrum to each other. Red and violet are not the most
different of all colour-sensations, as their spatial positions on the
colour scale might lead us to expect ; on the contrary, they are
as much alike as any two colours can be. Here again colour-
sensation and brightness-sensation are diametrical opposites.
The maximal differences of vibration-rate produce in the one
case similar subjective effects ; while in the other the extremes
of luminous intensity correspond to opposite qualities of sensa-
tion, black and white, between which the whole series of bright-
ness sensations is arranged in continuous progression. Now,
whatever hypothesis we adopt, we must seek to do justice to all
these peculiarities of sensation, besides taking account of the
laws of colour-mixture. Bearing that in mind, we arrive at
something like the following theory.

We may suppose that every retinal light-stimulation is com-

104 Lectures on Human and Animal Psychology

pounded of two separable constituents, — a colour-excitation and
a brightness-excitation. The brightness or ' achromatic ' excita-
tion may occur by itself. When that is the case, we sense black,
white, or grey. The colour or ' chromatic ' excitation always
implies the presence of the achromatic. When it occurs, we
sense saturated or whitish colour, according to the intensity of
the concomitant achromatic process. Differences in this latter
we may regard as ultimately conditioned by objective differences
in the intensity of light. It consists always of two qualitatively
opposite part-processes, one attending stimulation by light
and corresponding to the sensation of white, and the other
accompanying the recuperation of the retina after stimulation
and corresponding to the sensation of black. This part-process
of recuperation, you observe, is not only present when the visual

Weiss

Schwarz

FIG. ri.

organ is entirely free from stimulation, but accompanies the
more moderate degrees of stimulation, as a reaction of the
stimulated substance in the direction of restitution of the de-
composed chemical compounds. In the event of very weak
excitation, its intensity may even exceed that of the other part-
process, — that of stimulation. We can therefore represent the
system of brightness-sensations by a straight line, terminating
in black and white and having the various shades of dark grey,
grey, and bright grey arranged along its length in all their
manifold but perfectly continuous gradations. Such a line is
drawn in Fig. II. The opposed processes are represented by
vertical lines falling upon it, the intensity of the excitation-
process being shown by the length of the ascending verticals,
and the intensity of the recuperation-process by that of the

Theory of Light-sensations 105

descending ones. At absolute black the excitation-value must
be regarded as zero, while recuperation is at its maximum ; at
the brightest white recuperation is at its vanishing point, and
excitation at a maximum. Every intermediate brightness-
sensation presupposes a mixture of both processes. The total
physiological process corresponding to a mean grey, e.g., is com-
posed of a stimulation of the magnitude a w and of a recupera-
tion of the extent a s. These two part-processes do not cancel
one another, but intermix, so that in sensation grey is a quality
intermediate between those of black and white, and equally
related to both.

If we attempt to construct a similar geometrical diagram for
colour-sensations on the basis of their subjective peculiarities,
we must substitute for the straight line a curved one ; its two
ends must approximate, to indicate the subjective similarity of
red and violet. We may choose a circle, as the simplest line of
the description required. Then, as in Fig. 12, all the saturated
colours may be arranged round its periphery. But as the colours
of the solar spectrum leave a gap
between red and violet, we must
fill the series out by introducing
purple. Purple is obtained by
mixing red and violet, and all its
various shades lie between those
two qualities. The process of
chromatic stimulation, on the
principle of parallelism of sensa-
tion and physiological stimulation,
must be regarded as recurrent or
periodic ; the processes set up in IG> I2<

the retina by the quickest vibrations must resemble those
resulting from the slowest. You may find an analogy in the
octave. Although the ground-tone is further removed from its
octave than is any other tone of the chromatic scale, yet these
two are more nearly related in clang-character than any two
others. Indeed, this may be something more than an analogy.
The vibration-rate of the octave is twice that of its ground-tone,
and the vibration-rate of the light rays at the extreme violet
end of the spectrum is approximately twice that of the red rays

io6 Lectures on Human and Animal Psychology

At the same time, the conditions of light and sound-stimulation
are in other respects so different that the attempt occasionally
made to discover in the series of intermediate colours the exact
physical and sensational correlates of the principal intervals of
the tonal scale, — fifth, fourth, the two-thirds, etc., — has in every
case resulted in failure.

The great difference between colours and tones, which pre-
vents any such attempt from succeeding, is seen most clearly in
the different effects of the mixture of light and sound-waves.
When we mix sound-waves, we get a compound sensation, con-
sisting in the last resort of just as many simultaneously dis-
tinguishable elements as it contains successively distinguishable
tones. But when we mix light-waves, we always obtain a simple
sensation. White, which is composed of all the rays of the solar
spectrum, is in the last resort just as simple as is any colour
which contains but one single wave-modality.

These peculiarities of light-sensations lead us to two facts of
general import, which must be taken account of by any theory
of chromatic stimulation equally with the subjective similarity
of the terminal spectral colours. First, there may be substituted
for any simple colour a mixture of the two bordering colours
between which it lies. We can obtain orange from red and
yellow, yellow from orange and yellowish green, a pure green,
from yellowish green and greenish blue. Secondly, any colour
mixed with its subjective opposite in the right intensive propor-
tions gives us the sensation of white; the two are complementary
colours. The first of these facts indicates that the process of
retinal stimulation is not continuous, but graduated. For the
operation of any particular grade of vibration rapidity there can
be substituted the mutually supplementary actions of two other
grades not too remote from it, one of a less and one of a greater
rapidity. These combine to give an intermediate result. The
second fact, like the recurrent course of the colour-line, proves
that colour-stimulation is a circular process, in the sense that
every form of it is correlated with an opposite form ; so that
when the two excitations concur they cancel one another
leaving only the concomitant achromatic stimulation in sensation.
We can express this in our diagrammatic construction (Fig. 12}
by supposing the colours on the periphery of the circle to be so.

Theory of Light- sensations 107

arranged that the members of every complementary pair are
directly opposite to each other, and can be connected by a
straight line passing through the centre of the figure. At the
centre itself we may put white, and on the area between centre
and periphery write in the whitish colour-tones, as they gradually
change from complete saturation to absence of colour or
brightness.

All the simple qualities of visual sensation are contained in>
this figure, with the exception, first, of black and the greys
intermediate between it and white, and, secondly, of the blackish
or greyish colours, — brown, olive-green, etc. If these dark shades
of colour and brightness are to be introduced into the diagram,,
we must first draw a perpendicular to the centre of the circle,
white (Fig. 12), and arrange along its length the series of'

« 7 achromatic sensations, and,

Sdiwarz '

then fill in the dark colour-
shades and the intermediates
between them and grey or
black on concentric circles
placed at different heights
round the perpendicular line
of brightness-sensation (Fig.

OmwQ^VOWim*" coL withha ^ull? te£

the apex corresponding to
FIG. 13. black, the centre of the base

to white, and the periphery of the base to the saturated colours,
while all other qualities are distributed over and through the
body of the cone, their exact position being determined by
reference to the fixed positions of these fundamental qualities.

ENGLISH EQUIVALENTS OF GERMAN TERMS USED IN THE DIAGRAMS.

Blass, pale. Griin, green. Sch-warz, black.

Blau, blue. Hellgrau, bright grey. Strohgelb, straw-yellow.

Dunkel, dark. Himmelblaic, sky-blue. Violett, violet.

Fleischroth, flesh-coloured. Purpur, purple. Wasserblau, water-blue:

Gelb, yellow. Rosa, rose. Weiss, white.

LECTURE VII

;§ 1. RELATION OF THE SENSES OF SIGHT AND HEARING. § II. POSITIVE
AND NEGATIVE AFTER-IMAGES. § III. MECHANICAL AND CHEMICAL
SENSES. § IV. PHENOMENA OF CONTRAST. § V. GENERAL LAW
OF RELATIVITY.

§ I

IN the light of what we already know regarding the pro-
perties of sight and hearing, we can see that the best way
to understand the relation between these two senses is to turn
to their two essential differences. The first is this : that,
whereas a subjectively simple tone-sensation can only be caused
by a simple objective movement of the air, in the case of sight
any vibration of ether, simple and complex alike, produces a
simple light-sensation. And the second consists in the fact
that the simple tonal qualities can only be varied in two
•directions to produce higher and lower tones, whereas light-
sensations form two series, the chromatic and the achromatic,
•each consisting of a number of fundamental qualities and
intermediate tints, while the chromatic series, owing to the
subjective relationship of the terminal colours of the spectrum,
further constitutes a manifold of qualities which returns upon
•itself. The system of simple tones, therefore, can be represented
by a straight line ; that of light-sensations requires a figure of
three dimensions for its expression. Besides these general
differences, there are further distinctions dependent on various
properties which attach to the sense of sight, either exclusively,
•or to a greater extent than to any of the other senses.

If we produce a tone (e.g., by striking a string or tuning-fork),
-and then suddenly arrest the vibrations of the sounding body,

After-images* 109-

the tone-sensation immediately ceases. Even> if it actually lasts
somewhat longer than the stimulus, the duration of its after-
effect is so short as normally to escape our notice. It is quite
different with the sensation of light and colour. You know
that if a red-hot ember is swung round at a moderate rapidity,
you see a complete circle of fire. This phenomenon shows that
the light-impression in the eye must persist at least during the
time that the ember takes to pass from any point in its course
back again in a circle to the same position! We can obtain,
more exact knowledge of the after-effect of light-stimulation by
fixating a luminous object for some time and then suddenly
closing the eyes. We then see on the dark field of vision an.
after-image which resembles the object, but which gradually
undergoes very curious changes as regards its- light and colour-
properties. For the first moment it is exactly like the external
object, then its intensity decreases somewhat, and again after a
little time its quality alters to just the opposite of the original.
If the fixated object were white, the after-image turns black, —
darker, i.e.t than the dark field of vision on which it is seen, — if
the object were black, the after-image becomes white, brighter
than the surrounding field of vision. Finally, if the impression
were coloured, the after-image assumes the complementary-
colour, greenish if the object were red, reddish if it were green.
In its first stage, therefore, the after-image is called positive or
s ame- coloured \ in its later phases, negative or complementary.
Both phenomena, but especially the more persistent comple-
mentary images, are observable with open eyes> if the object
fixated is extremely bright. If you glance, e.g.,. at the setting
sun, and then look at the roadway or a grey wall, you may see
a clear green after-image of the solar disc at the point of fixa-
tion.

The phenomena of after-images prove, in the first place, that
the stimulation-process in the retina outlasts the external
stimulus by a considerable period, often amounting to several
seconds. But they show also that the stage of direct continu-
ance of stimulation, which is manifested in the positive after-
image, is followed by an opposite condition of the sense-organ
during which bright objects are seen as dark, and dark ones as
bright, and in general every colour as its complementary.

I io Lectures on Human and Animal Psychology

This complementary after-effect may be easily explained 0:1
the assumption of a partial exhaustion of the retina. If, e.g.,
our sensibility to red is exhausted at a particular place, we
shall see white light at that place just as if no red rays were
affecting it ; in other words, since the subtraction of red from
white gives green, a red object will leave behind on the exhausted
retina a greenish after-image. The quality of these comple-
mentary after-images may be enhanced by contrast with its
background. This holds especially of the cases mentioned
above, where the after-images of white and black objects were
observed upon a dark field of vision.

§ HI

These striking differences in the after-effects produced by
stimulation of the two sense-organs render it probable that the
processes which excite the sensations of tone and light are
totally different in character. Indeed, it seems probable that
sound vibrations set up corresponding vibrations in the
membrane of the cochlear canal, in which the fibres of the
auditory nerve terminate ; and that our separate perception of
the constituent tones of a clang is due to the tuning of the
individual fibres of this membrane to various tones. The
stimulation-process would, therefore, here be a mechanical one,
and the sensation is consequently interrupted as soon as the
vibratory movement of the stimulated fibres ceases. That
must, of course, occur very soon after the cessation of the
external air vibrations which set up the excitation. It is
probable, once more, that the rapid arrest of the vibrations of
the membrane is promoted by the action of certain solid
cuticular structures, semicircularly arranged, which rest upon
it, and whose function must be analogous to that of the damper
of a pianoforte. But when a light-stimulus affects the retina,
we have obviously a very different state of affairs. There are
many observations which go to prove that the sensitivity of the
retina to light is like that of the prepared plate in the dark
room of a photographer. One of the most striking is this : in
the dark, the retina is of a deep red colour ; exposed to light,
it gradually bleaches, and finally turns white. This renders
it practically certain that light-stimulation is a photochemical

Mechanical and Chemical Senses \ 1 1

process. Such processes play an important part in organic
nature ; e.g., in the breathing of the green portions .of plants
and in the production of the colours of flowers. Now a chemi-
cal process, even if it is comparatively soon over, always
requires a considerably longer time for its completion than does
a simple transmission of motion. Regarded from this point of
view, the after-image appears simply as a subjective indication
of the duration of a photochemical action ; and its two phases
point to the fact that there are two processes which run their
course during that action. The positive after-image gives us
the duration of the chemical decomposition occasioned by the
light-stimulus ; the negative or complementary after-image
shows us an after-effect of this decomposition. This latter is a
phenomenon analogous to those of exhaustion in other living
organs, — e.g., in nerve and muscle, — all alike manifest themselves
in decreased excitability for stimuli of the same kind as those
previously operative.

The senses of sight and hearing may, therefore, be regarded
as the principal representatives of two fundamental forms of
sensory excitation, — the mechanical and the chemical. In setting
these expressions over against one another, we must be careful
not to refer them to processes in the sensory nerves. These
consist, probably in every case, of very rapid chemical decompo-
sitions. Our purpose is merely to discriminate between the
different ways in which external stimuli affect the nervous
terminations in the organs of sense. With the mechanical
senses may probably be reckoned (besides hearing) that of
cutaneous pressure, as is shown by the brief continuance of the
after-effect of impression in sensation. To the chemical senses
belong (besides that of sight) the cutaneous temperature-sense
and the senses of smell and taste. The organ of touch is the
earliest, and in the lowest forms of organic life the only, sense-
organ. And the fact that it includes both a mechanical and a
chemical sense is, perhaps, not without significance for the
physiological history of the development of sense-functions.

§ IV

The phenomena of negative and complementary after-images
which we have been discussing require little more than purely

H2 Lectures on Human and Animal Psychology

physiological explanations. There is, however, a very large
number of cases in which our sensations of light and colour
undergo change where this cannot be derived from the after-
effects of stimulation and from the influence of exhaustion, or
where at least these phenomena afford only a partial explana-
tion. Of course, wherever after-images manifest themselves at
the same time, they may be explained in physiological terms.

If we cause light to pass through a sheet of red glass, and
then cast a shadow somewhere upon the red illuminated surface,
we ought really to see this shadow grey. For it contains nothing
but diffused white light, the intensity of which has been lessened
by the shade. As a matter of fact, however, the shadow looks
not grey, but green. This same green tint may sometimes be
observed in nature, in the shadows cast by trees, when the
setting sun gives a reddish light in consequence of the stronger
absorption of the refrangible rays by the atmosphere.

An experiment which exactly reproduces the conditions of
this subjective colouring of natural shadows can easily be made
by means of the colour top and the rapidly rotating discs which
we employed to illustrate the mixture of colour-sensations. We
take a disc with small coloured sectors on a white background.
Somewhere about half-way between the centre and periphery,
the coloured sectors are replaced by narrower portions of a
black band (Fig. 14). If we let the top rotate at a high speed,
the colour of the sectors fuses with the white of the background
to a whitish tint ; and where we inserted our black bands, we

get a mixture of black and white, i.e.t
grey. This grey, you see, corresponds
completely to a circular shadow cast
upon the coloured background. But
this objectively grey ring does not
appear to us as really grey, but as
coloured, and as coloured comple-
mentarity to the background. If the
sectors are green, the ring looks red ;
_ if they are red, we see it as green, etc.

Here is a still simpler experiment.
Take a sheet of thin white notepaper and a sheet of coloured
paper of the same size ; lay the white paper on the coloured

Phenomena of Contrast 113

so that it exactly covers it ; and then push a little square of
grey or black paper between the two. If the coloured paper
which is underneath is green, e.g., its colour shines through the thin
notepaper, except at the place where the grey square lies. This
should appear grey, but, as a matter of fact, looks red. If our
coloured paper had been red, the grey square would have looked
green. In short, it always takes on that colour which, mixed with
the colour of its surroundings, would produce white. The pheno-
menon is not so striking, but yet clearly apparent, when you
simply lay a piece of grey paper on a coloured background, with-
out covering it with the thin notepaper. Suppose, e.g., that you-
cut little squares from the same grey paper, and lay them upon
red, green, yellow, and blue papers, placed side by side. They
all look different ; that on the red is greenish, that on the green
reddish, that on the yellow bluish, that on the blue yellowish.
And the effect of the background is just as obvious, if you em-
ploy colourless lights of various brightnesses, instead of colours.
Fasten two similar grey squares upon black and white sheets of
paper respectively ; the former appears so bright as to be almost
white : the latter looks dark, and under favourable conditions
may approach to black.

In describing all these phenomena and enumerating their
conditions, we have left out of account one important factor, —
the extent of the surfaces employed. If the shadow cast in
coloured light is very large, the centre will look grey ; only at
the edges will its colour become apparent. We can best show
the dependency of subjective colouring upon the space-relations
of the surfaces compared by having recourse again to revolving
discs. We furnish a disc with sectors in the way shown in Fig.
1 5 ; the sectors are cut into steps, the absolute magnitude of
which is in every case the same.
If now the sectors (£>) are blue,
and the background (£) yellow,
we shall expect, when the disc is
rotated, to see a bluish-yellow mix-
ture, which is perfectly uniform
within each step of the sectors B,
but which is changed from step to

step in such a way that the yellow

FIG. 15.

H4 Lectures on Human and Animal Psychology

predominates more and more in the mixture as we approach the
periphery ; for objectively the colour of each step remains the
same throughout its whole extent. In reality, however, the
inner and outer borders of each blue-yellow ring are differently
coloured, and the intermediate points show a gradual transition
from one shade to the other. Each of these constituent colours
shows most strongly when contiguous to a ring which contains
less of it in its mixture. On our own disc, therefore, the outer
edge of every ring is blue, and the inner yellow. We have, that
is, a succession of yellow and blue rings outlined upon a back-
ground of mixed colour.

The same experiment can be made in a different way. We
will take a white disc and paste upon it not coloured, but black,
sectors, as has been done in Fig. 15. We should expect to
obtain by rotation concentric grey rings, increasing in brightness
toward the periphery of the disc, but showing no variation within
each ring. We find instead that all the rings look brighter on
the inside, where the contiguous ring is darker, and darker on
the outside. The difference is so great that the brightness of
the different rings oftentimes appears to be the same through-
out ; so that when rotated rapidly the disc seems to be com-
posed simply of alternating black and white circles.

These experiments illustrate a group of phenomena to which
the general name of contrast phenomena is given. The name is
an obvious one, for their principal condition is clearly the oppo-
sition of two colours or of two degrees of brightness. And for
the same reason the subjective colour due to this opposition (the
green tint of the shadow in red light) is also termed contrast
colour. We may, therefore, use the expressions 'contrast colour'
and ' complementary colour ' as synonymous.

The identity of these two concepts has been the chief agent
in determining a large number of physiologists to refer the
phenomena of contrast to like causes with complementary
after-images. Just as the after-image arises from persistence of
the excitation in the stimulated region of the retina, so contrast,
they say, is a result of a diffusion of excitation over the sur-
rounding portions of the retina. This analogy is, of course,
condemned at once by the fact that we distinguish a positive
after-image, resembling the original stimulation, from a negative

Phenomena of Contrast 115

phase of it, which is opposed to the former ; while the effect of
contrast is always negative and antagonistic. Moreover, a con-
siderable time is necessary for the development of the after-
image, whereas the contrast change of sensations is instanta-
neous. But we have still other and weightier reasons to urge
against the analogy. A spatial diffusion of stimulation should
appear in more intensive form the greater the strength of the
original stimulus. This is, however, not by any means the case.

A weak stimulus may under favourable circumstances bring
about a stronger contrast than a strong stimulus. This we
learned from our experiment with colourless objects laid upon a
coloured background. You remember that if we cover them with
transparent notepaper, the contrast is much more obvious than if
they are left uncovered, — though their colour is weakened by the
covering sheet. This suggests that contrast-effects in general may
consist not in a direct alteration of sensation, but in changes in our
subjective mode of apprehending sensations ; and the suggestion
is fully confirmed by other observations. Let us vary our last
•experiment a little. By the side of the grey square, which has
taken on the colour complementary to its background, we place
a second square of exactly the same brightness. Now that com-
parison of the two is possible, the contrast colour disappears,
but it reappears so soon as the second grey is removed.

Since the comparison of impressions is so plainly important in
this connection, it has been maintained, as against the physio-
logical hypothesis mentioned above, that contrast depends upon
a deception of judgment. A shadow seen in red light looks green
to us, it is said, because we are accustomed to regard ordinary
diffuse daylight as white, and to judge of colours in comparison
with it. So that if in a particular case it is not white, but red, a
shadow cast in it must seem to us to be green ; for if reddish
light looks white, light which is actually white will be no longer
regarded as such, but will necessarily appear to have had a cer-
tain quantum of red taken from it, i.e., will seem greenish. If
we mix all the colours of the spectrum together with the excep-
tion of red, we obtain, of course, a green shade. The same prin-
ciple of wrong judgment is employed to explain the facts
observed in the experiment with transparent paper. If we lay
a transparent white sheet upon a dark red one, it looks bright

n 6 Lectures on Human and Animal Psychology

red. Now we push our grey square in between the two sheets.
This, of course, renders that portion of the surface colourless ;
but we judge that the bright red paper extends over it also, and
so see it in the colour which an object must possess if it is to
appear colourless when seen through a red medium, i.e., as green ;
or, to put it more generally, we see it in the colour complement-
ary to that of the transparent covering.

Now there are weighty objections to be urged against this
derivation of contrast phenomena from deceptions of judgment.
First of all, it is not right to say that because we are accustomed
to see diffuse daylight white, therefore we must do so in the ex-
ceptional cases when it is not really white, but coloured. We see
clearly enough that the illumination of the setting sun is reddish,
and we are not in the least inclined to regard the light that comes
to us through a sheet of coloured glass as white ; we sense it
precisely in its own proper colour. These instances serve to show
that the assumption from which the explanation proceeds is not
justifiable. And consider, furthermore, how extraordinarily com-
plicated this series of inferences is, in terms of which we are said
to sense. In the experiment with transparent paper, e.g., we are
not only supposed to take account of the actual colour of the
objects seen, but also of the influence of the medium through
which the light rays have to pass before they reach our eye.
And yet the experiments may be easily performed under con-
ditions which definitely exclude any such influence. We have
already seen that the contrast is also apparent when we lay our
grey square directly upon the coloured background. Now, if
pains are taken to choose saturations and brightnesses exactly
corresponding to the modified colour and brightness appearing
in the former case through the transparent paper, the contrast is
just as clearly observable as before. So that it is not by betray-
ing us into a false judgment that the transparent medium
heightens contrast, but rather by producing degrees of satura-
tion and brightness, which are especially favourable for it.
Colour contrast always appears most strongly when the coloured
object and the colourless one which it tinges by contrast are as
nearly as possible of the same brightness. This condition is
more nearly realised in all cases where the brightnesses of the
objects are originally different, and their relations consequently

Phenomena of Contrast 117

not so favourable for the production of contrast, by the use of
the transparent paper as a covering.

But although the judgment theory is untenable, the expression
'comparison ' has a certain justifiable application to the process
underlying contrast. We observe that not only is a really grey
object modified by its surroundings so as to appear complement-
arily coloured, but also that this contrast colour disappears as
soon as we destroy the influence of the surroundings by intro-
ducing another object of the same grey colour. It is, therefore,
not amiss to say at least that this removal of contrast is the
result of a comparison ; and if the expression is permissible in
this case, it must be so also for our original phenomenon. For
it is, indeed, conceivable that the result of one comparison could
be cancelled by that of another, but hardly that an excitation-
process due to definite physiological causes could be annulled
by such an act. If we objectively tinge a grey paper with green,
no amount of comparison of it with a pure grey of the same
brightness can deceive us with regard to the existence of the
colour. And we learn from the phenomena of after-images that
a colour due to subjective retinal excitation behaves in this con-
nection just like one objectively produced. But apart from these
considerations, there is nothing at all in the phenomena of con-
trast which is not done full justice to by this reference to a rela-
tive comparison. A grey paper on a black background looks
brighter than it does upon white. This is perfectly intelligible
if we assume that our apprehension of a particular light-sensa-
tion is not something absolutely unalterable, but is dependent
upon other light-sensations which are at the same time present
in consciousness, and in relation to which it is, so to speak,
measured. The same point of view may be adopted for the ex-
planation of colour contrast If we gradually decrease the satu-
ration of any colour, it passes over finally into white or grey.
We may therefore regard the absence of colour as the lower
limit of the various stages of saturation of any given colour.
The principle of relativity which we have just been discussing
renders it inevitable that the saturation of a colour should be in-
creased, if its surroundings, presented at the same time with it,
are complementarily tinged. This being so, the minimum of
saturation will, like every other degree, pass over into a more

Ii8 Lectures on Human and Animal Psychology

complete saturation ; i.e., a colourless surface will in contrast to a
colour appear complementarily coloured.

The notion of comparison is, therefore, generally applicable
to the mental process underlying contrast. But the judgment
theory is wholly wrong in regarding the process as a compara-
tive judgment, for the production of which all manner of com-
plicated reflections have to be called into account. When it is
said that these reflections take place unconsciously, a suicidal
admission is made. At the same time that the mental process
is resolved into logical reflections, it is really granted that these
reflections do not actually exist, but only represent the transla-
tion of a process of an entirely different kind into the form in
which we usually cast our reflections. Now such a translation
is quite allowable when it is simply used as a means of making
intelligible the mode of operation of the elements which have
been empirically shown to be present in some particular process.
But though allowable to a certain extent, for the sake of clear-
ness, this method of interpretation oversteps its rightful limits
when it leads us to ascribe to judgment purely imaginary pre-
liminary stages, such as, e.g., the reflection how a colour ought
to appear when it is seen through another colour. That is what
it does, you see, in the logical theory of contrast which we have
been discussing, — logical : for the theory is really logical, and not
psychological. If we wish, therefore, to retain the concept of
comparison to designate the processes under discussion, we shall
only be able to mean by it an associative comparison ; i.e., a con-
nection of two sensations, where the quality of each is deter-
mined by its relation to that of the other.

§V

We have thus referred the phenomena of contrast to the
same principle of sensational relativity with which we are
already familiar as the general psychological expression for the
facts of Weber's law. Our apprehension of stimulus-intensity
or of tonal pitch is not something absolute, but depends upon
the character of other stimuli and tones with which we bring the
given sensation into relation. In the same way, the subjective
effect of a particular light and colour is determined by the rela-

General Law of Relativity. 119

tions in which they stand to other impressions of light and
colour which are affecting us at the same time.

We may now subsume all these phenomena — tonal intervals,
light contrast, the geometrical increase of stimulus-intensity for
equally noticeable sensation-differences — under one general law :
the law of relativity. The psychological significance of them all
is the same. We may formulate this law, which may be re-
garded as the most general expression of the results of our psy-
chological analysis of sensations, as follows : wherever tJiere
occurs a quantitative apprehension of sensations, whether as re-
gards intensity or degree of quality, the individual sensation is
estimated by tJie relation in which it stands to other sensations of
tJie same sense-modality.

Sometimes this relative estimation of particular sensations is
determined by the impressions which immediately precede or
follow it ; this is usually the case in the measurement of equally
noticeable stimulus-differences. Sometimes it is determined by
sensations simultaneously present, as well as by those coming
before and after ; this is the case with tone-pitch. Sometimes
finally, only the simultaneous impressions come into account, as
in light and colour contrast. Which of these three conditions is
fulfilled depends upon the special circumstances of the experi-
ment, and upon the peculiarities of the special sense with which
we are dealing. The matter does not at all affect the signifi-
cance of the law. And this significance is, you see, predomi-
nantly psychological. For the most obvious interpretation of the
law is this : that we never apprehend the intensity of a mental
state as if it stood alone ; we never estimate an isolated magfni-

* o

tude ; but measurement implies a direct comparison of one con-
scious state with another. And so we shall expect to find that
the law of relativity is not restricted to the sphere of sensation,
but is applicable in every case where the intensity of a mental
process is quantitatively apprehended and compared with that
of others.

LECTURE VIII .

§ i. REFLEX MOVEMENTS. § 2. PURPOSIVENESS OF THE REFLEX.
§ 3. DEVELOPMENT OF THE REFLEXES OF TOUCH AND SIGHT.

§ I

WE have seen 'that sensation is the ultimate source of a
very large number of the concrete processes that go to
make up our mental life. Everything that we meet
with in our world of ideas is derived in the last resort from sen-
sations, and ideas are the raw material of all the higher mental
activities. It may be questioned whether the stream of thought
could not continue without any reinforcement from the outside
world ; but this at least is certain, that it has its source in sensi-
bility, and that sensibility does perpetually interfere to deter-
mine its direction. In this way our investigation of sensation
leads on directly to the consideration of a second and very
important psychological problem, — the problem of the composi-
tion of ideas from the sensational elements that enter into them
in so great number and variety.

In our previous discussions we examined the physical con-
ditions of sensation, external sense-excitations, before we pro-
ceeded to sensation itself. Now the further question arises :
what is the immediate consequence of a sensation ? Observation
furnishes us with the unhesitating answer : every sensation
which is of sufficient intensity and not inhibited by opposing
influences is followed by a muscular movement. This muscular
movement we term a reflex movement, and the name is appro-
priate. There have plainly taken place a transference of nervous
excitation within the central organs of the nervous system from
sensory to motor fibres, and a similar transmission of stimulation
from these to their particular muscles : the stimulus is, as it
were, thrown back, reflected. Reflexes are observed so long as

Reflex Movements 121

the nerves of sense retain their connection with the central
organs of the nervous system, and these remain united by motor
nerves to the muscles. But it is not necessary that the whole
•central nervous system should be capable of exercising its
normal functions. The cord may be severed from the brain, and
reflexes still be mediated by the nerves which enter it ; indeed,
quite a small section of the cord will suffice for the necessary
transference of excitation.

This transmission of stimulus by the sensory to the motor
nerves is provided for in the elementary organisation of the
•nervous system. If we examine brain and cord microscopically,
we find, first, a number of nerve-fibres of varying thickness,
continuations of sensory and motor nerve-trunks, and secondly,
besides these, cells of varying size, — viscous structures, like most
organic cells, containing a more solid nucleus and a number of
small granules. These nerve-cells are characteristic of and
peculiar to the central organs of the nervous system. How
important they are functionally you may judge from the fact
that they always stand in connection with both incoming
(afferent) and outgoing (efferent) nerve-fibres. As a rule each
one sends out several nerve-fibres. We may look upon these
cells, then, partly as ultimate terminal organs, partly as organs
for the mediation of connection between conducting fibres. To
make the mechanism of the reflex clear, we have
only to suppose a nerve-cell interpolated be-
tween two fibres, one of which (e] leads from a
sense-organ, the other (ft) to a muscle. We
have there the scheme of the reflex. As a
matter of fact, however, the nervous connections
are very much more complicated and involved,
as we should expect, knowing what we do of the
complexity of structure of the central organs. FlG- l6-

The intensity and extent of the movement constituting the
reflex response to a sense-stimulus are enormously different in
different cases. In general they increase with increase in the
intensity of stimulus. The very weakest stimuli do not as a
rule excite reflex movements at all ; moderate intensities arouse
a. moderately intensive movement, confined to some particular
group of muscles ; as the intensity of stimulus is further in-

122 Lectures on Human and Animal Psychology

creased, the reflex answer becomes more general, till it finally
involves practically the whole organism. This law of the in-
crease of reflex movement with increase of stimulus remains
constant despite the fact that individual and temporal differences
may be by no means inconsiderable. These are mainly referable
to varying excitability. The more excitable the sensory nerves
and nervous centres, the earlier does the reflex make its appear-
ance, and the more quickly does it run through the gamut of its
intensive and extensive changes. Again, it may be intensified
or reduced by the action of various influences upon the organism.
Beheading, removal of the brain, increases the reflexes, until
death occurs. Many amphibia may be kept alive for months
after beheading, and their reflex excitability is throughout this
whole period abnormally great. There are also certain chemical
substances the effect of which upon the nervous tissue of the
central organs is to occasion a decided intensification of the
reflexes. Besides some alkaloids, whose influence is not very
great, we may especially mention strychnine in this connection.
It produces such an excess of sensibility that the lightest
pressure upon the cutaneous nerves, such as normally would fail
to arouse any movement at all, brings on reflex twitchings over
the whole body. In deep sleep or swoon, on the other hand, the
reflex excitability is diminished, as it is by the influence of opium
and other cognate poisons.

What the chemical changes within the nerve-cells are upon
which the influence of strychnine and similar poisons depends is
still unknown. But their general effect may be easily deduced
from the universal laws of the action of forces. It cannot be
supposed that a material heterogeneous to the constituents of
nervous tissue creates fresh nervous force. The only tenable
hypothesis is, that it facilitates the actualising of forces already
latently present ; i.e., that it overcomes certain of the inhibitions
making against the transformation of stored into kinetic energy,
and so renders the transforming force more effective. Substances
of an opposite nature will, on the contrary, increase the number
of inhibitions, and thereby increase the amount of external force
necessary to release the cell from its state of tension. You will
understand this easily enough if you take a simple mechanical
illustration.

Reflex Movements 123

Suppose that you have a clock whose movement can at any
moment be arrested or started by the throwing in or out of gear
of some mechanical appliance, say a spring, which stops the
works or not according as it is tightened or relaxed. So long
as it is tightened, the weight which moves the clock will be
exerting a pressure against it. This represents the stresses to
which the mechanism is subject. As soon as it is relaxed, these
are transformed into energy of motion. To effect the relaxation
some small sum of work must be expended. Its magnitude will
be proportional to the resilience of the elastic spring, and it can
very easily be increased or decreased by varying the tension of
the spring.

The movement of the clock in this illustration is the reflex
movement, the relaxation of the spring is the operation of au
sense-stimulus, and the greater or less tension represents the
influence of the substances which are exerting a specific action
upon the mechanism of transformation of energy. Just as a
greater tension of the spring increases the difficulty of starting
the clock, so the alteration produced by opium in the nervous
system makes against the release of a reflex movement ; and
just as a less degree of tension facilitates the starting of the
clock, so strychnine facilitates reflex movement. Every clock
goes for a certain period, at the expiration of which it runs down
and requires to be rewound ; in other words, there is in it a
certain amount of potential energy which it takes a definite time
to use up and transform into energy of motion, and which then
requires renewal. Without this renewal the clock cannot go-
any more. Here again there is a complete analogy with the
mechanics of the nervous system. There is a definite amount
of potential energy contained in the central organ. This is,
partly, only renewed when it has been almost exhausted (as irt
the clock), the restoration taking place during sleep ; but, partly,
there is a continual process of renewal, as, indeed, there must
be, if the chemical composition of the nervous elements is not to
be so radically disturbed that a return to the normal condition
is altogether impossible. So that the inevitable result of too
heavy a draft upon the potential energy is death. Strych-
nine and similar poisons bring on death simply by exhausting
the energy of the central organs, and particularly of the cord..

"124 Lectures on Human and Animal Psychology

The other tissues of the body are left uninterfered with; and
even the nerve-fibres, as has been shown by their severance from
the cord, remain capable of taking up and transmitting stimuli.
Now the removal of the brain has the same effect upon the
reflexes as any one of these poisons, which helps to set the
reflex mechanism in action. But it is plain that this effect must
be differently produced. The facts are these. The nerve-cells
of the cord, which connect sensory with motor fibres, are them-
selves very complexly interrelated, and, moreover, send out fine
nerve-fibres which run to the brain, and there terminate in the
central cell plexus. These relations are represented schematic-
ally in Fig. 17, where r r are cord-cells, functioning as reflex

centres, and cc central brain-cells. The
stimulus acting on the termination of
a sensory nerve (eef) is not simply
transmitted by way of the reflex arc to
a motor fibre (bb'\ but is conducted to
the higher cells (cc), and there diffused
— it may be with practically no check
or restriction. The figure shows,
moreover, that a single sensory fibre is
r not always correlated with a single
motor fibre. The conduction paths
IG> I7' between cell and cell are so numerous

that every sensory fibre is connected with a number of motor,
-and even with other sensory, fibres. So that if an excitation
-arises at e, we shall expect force to be released not only in b,
but also in b' and /. To get any idea at all of the organization
of the central organs you must multiply these schematic connec-
tions indefinitely. A sense-impression will result not only in
the movement of a definite group of muscles, but in movements
and sensations at quite different parts of the body, extending
perhaps to a whole number of muscle groups and to several
sense-organs.

There can, indeed, be no manner of doubt as to the existence
of reflected sensations, — sensations occasioned not by the stimu-
lation of their own sensory nerve, but by that of some other.
Normally, it is true, they are very weak ; and it is only in
•conditions of pathologically increased excitability that they

Reflex Movements 125.

attain to a more considerable intensity. They appear, then, to-
be essentially different from reflex movements in that they
are never so intensive as the directly stimulated sensations, but,
as a rule, only perceptible at all with strained and careful atten-
tion.

Far more important is the other side of the matter, — the ex-
tension of the reflex movement due to the transmission of the im-
pulse given by sensation to parts of the body increasingly remote
from its origin. Heightening of stimulus-intensity will produce
a very considerable diffusion of movement, but the quite
universal reaction is only gained in conditions of abnormal excita-
bility, e.g., under the influence of strychnine. Here there is no
definite limit set to the extension of the reflex response ;.
practically all the muscles of the body are violently convulsed
during the action of the sense-stimulus.

But, these abnormal states apart, we can assign definite rules
to the diffusion of the reflex. It is uniformly dependent upon,
intensity of external stimulus. When the stimulus is only just
intensive enough to call forth a reflex answer, the movement
is always restricted to the group of muscles most immedi-
ately connected with the sensitive part. If it is the retina
that is stimulated, the resultant movement is exclusively eye-
movement ; if it is the skin of one of the four limbs, only
that limb moves ; if it is some portion of the skin of the head
or trunk, there is movement in the nearest muscle group, and
generally also in the limb which bears the closest relation to-
the stimulated spot. Thus a weak stimulus applied to the left
cheek leads to a contortion of the left side of the face and a
movement of the left arm. • The four limbs, which with the eye
constitute the most motile parts of the body, are most liable to-
be thrown into movement by cutaneous stimuli.

If the intensity of stimulus increases, the reflex movement
becomes more widely diffused, but is still confined for some
time to muscles in the neighbourhood of the organ stimulated.
Thus it may extend from one leg or arm to the other. As the
intensity increases further, the response grows more and more
general ; at the very highest intensity all four limbs are generally
in motion together. The movement is at first a flexion, but is
changed to extension at the highest intensities. This fact, —

126 Lectures on Human and Animal Psychology

that a stimulus which affects all the motor fibres equally always
gives rise to a movement of extension, — seems to show that
nerves of the extensor muscles are not so intimately connected
with the sensory fibres as those of the flexor muscles. It is not
till the stimulus becomes very intensive that the extensors are
affected, though when once the reflex response has become
maximal, extension tends to get the upper hand of flexion.

In both of its two principal forms, the reflex possesses the
characteristic of purposiveness. If the movement is restricted to
the muscle group underlying or immediately adjoining the point
stimulated, its result is to free the part affected from the influence
of the stimulus. If the response is more diffuse, the action of the
muscles is primarily auxiliary to the movement of escape ; and
it is only in extreme cases, where a whole number of muscle
groups are thrown into movements of extension, that all evidence
of purposiveness is absent.

The principal reason for this purposiveness of character is
that the reflex movement is usually directed towards some
end, and ceases when it has been attained. The end is contact
with the part stimulated. If you stimulate a headless frog by
applying a sharp point to the posterior portion of the trunk, one
of the legs is violently moved towards the injured spot Con-
tact with this seems to be the end of the whole movement ; and
contact is effected in the simplest possible way, — by that limb
and by those muscles which can mediate it with the least ex-
penditure of effort.

Stimulation of the eye produces results analogous to those
obtained by stimulation of the skin. If you look at the eyes of
a new-born child, you cannot fail to notice the fixity of their
gaze. The eye moves, it is true, and especially if light-stimuli
fall upon it ; but the movement is altogether irregular, and there
seems to be no definite connection between it and the locality
of the visual impression. This relation is only gradually built up
If you bring a light into the visual field of a child several days
or weeks old, you will find that it turns its eyes towards you and
looks fixedly at the light. If you introduce two or more lights,

Purposiveness of the Reflex 127

it generally alternates between one and the other. But its gaze
is riveted upon the light ; the eye is held to that by a kind of
mechanical necessity, and can only leave it when its impression
is weakened by fatigue, or when some other stimulus has
appeared to oust it. We are in presence, that is, of a similar
phenomenon to that of the touching of the stimulated part of
the skin by means of a reflex movement. When a light-stimulus
makes its appearance in the field of vision, the eye moves
towards it, just as the hand moves towards the irritated spot
upon the skin.

We must notice, however, that the reflex mechanism of the
eye is twofold. On the one hand, there is the connection
between light-sensation and the muscles that contract the pupil
and close the lids ; on the other, that between light-sensation
and the muscles which move the eyeball. The lid reflex may
be occasioned by quite weak light-stimuli, if the eyes have
previously been in the dark. Thus the first opening of the eye
of the new-born child to light is at once followed by a violent
and convulsive closing reflex. But the organ very quickly
begins to grow accustomed to the light ; and then the connec-
tion between light-sensation and muscles of the eyeball makes
its appearance. At first, as we have seen, the entrance of a
light-stimulus into the field of vision merely produces move-
ment ; we cannot say that the movement is governed or directed
in any way. It is still only an uncertain groping for the light.
But between the second and fourth weeks after birth some
amount of regularity is observable. The child begins to fixate ;
and every light-stimulus that appears within the field of vision
excites a tendency to fixate it. Fixation consists in the as-
sumption by the eye of the position in which a definite light-
impression forms an image upon the most sensitive portion of the
retina. This spot lies approximately at the centre of the whole
tinal surface, a little to the outside of the point at which the optic
nerve enters the eye, and from which it radiates over the retina.
It is characterised anatomically by an extremely close packing
of the retinal elements which take up the light-stimulus, and by
a yellow coloration. On this latter account it is commonly
known as the yellow spot.

The way in which the reflexes of the eye develop, then, is

128 Lectures on Hitman and Animal Psychology

this. First of all, light-stimuli excite merely irregular move-
ments. After a time, these take on a definite form, and serve a
definite purpose : the eye moves in such a way as to bring the
image of the stimulating light upon the yellow spot. If at this-
stage a light moves to and fro within the field of vision, the eye
follows it with an equally continuous movement.

By what steps does this regularity emerge from the initial
irregularity ? It is clear that the determinate relation of the
yellow spot to the reflex movements cannot be given in the form
of an interconnection of the nervous elements conditioning
them. If that were the case, the first ray that fell upon the
retina would release a reflex movement of the same character
as those which we observe later. Now, apart from the evidence
against this view that is furnished by the facts of experience,
there is nothing to suggest it in the manner in which the force
which releases the movement is transmitted within the central
organs. The force transmitted from the sensory to the motor
fibres is dependent as regards intensity and diffusion upon the
intensity of stimulation, and the temporary condition of the
organs which subserve its transmission. So that there is. no-
reason why an intensive stimulus in the neighbourhood of the
yellow spot should excite only a very slight eye-movement,
while a weak stimulus at the periphery of the retina is followed
by an extensive one. No ! there must obviously be influences
at work during the development of the sense which gradually
bring it about that, while the release of a reflex movement is
effected by the physical mechanism, its extent and direction
depend entirely upon the place of the part stimulated ; so that
the greater sensitivity of the organ or the increased intensity of
stimulation can only find expression in a greater energy and
rapidity of movement. To obtain a complete explanation of
how this happens, we must look a little more closely at the
structure of the sense-organs.

§ HI

The skin over the entire surface of the body is sensitive to
stimulation. And the entire retina is similarly sensitive, with
the exception of the place of entry of the optic nerve, where

Development of Reflexes of Touch and Sight. 129

there are none of the peculiar end-organs which subserve vision.
But the sensations derived from various parts of the skin or
retina are by no means entirely similar. So far as the skin is
concerned, you can convince yourselves of this very simply.
Touch your cheek and the palm of your hand with your ringer,
being careful to exert the same amount of pressure in each case.
The two sensations are quite clearly different. And it is just
the same if you compare the palm with the back of the hand,
or the neck with the nape, or the chest with the back, or any
two portions of the skin which are some little distance apart.
More than that, if you observe carefully, you will find appreci-
able differences in the quality of sensations coming from portions
which are fairly close together. As you pass from one point
upon the sensitive surface to another, you experience a gradual
and continuous change in cutaneous sensation, although the
nature of the external pressure has remained perfectly constant.
Even the sensations from corresponding places on the two
halves of the body, alike as they are, are not altogether the
same. If you touch first the back of one hand, and then that of
the . other, you find that there is a slight qualitative difference
between the two sensations.

A similar variation can be shown to exist in the retina. Fix-
ate a piece of red paper held in the hand, and then move it
slowly away, without allowing your eye to follow it as it disap-
pears. Its image falls at first, of course, upon the yellow spot ;
and then travels across the retina towards the periphery. You
will observe that during the lateral movement of the object the
sensation of red undergoes a gradual change : the colour-tone
becomes darker, appears to take on a tinge of blue, and finally
passes over into pure black. Any colour that you choose, as
well as white, will show similar alterations. The last stage in
sensation is always black.

The obvious explanation of this phenomenon is, that we sense
differently with the different parts of the retina ; and that the
sensation gradually changes as the impression moves from its
centre towards the outlying regions. So far as we can tell, the
alteration takes place in just the same manner whatever the
direction of movement ; but, — and this is noteworthy, — it takes
place with different rapidity in different directions. If the object

K

130 Lectures on Human and Animal Psychology

moves from the centre outwards or upwards, the series of colour-
tones is passed through more quickly than if it moves inwards
or downwards ; so that a body imaged on the outside or upper
portion of the retina looks black, while if its image falls on a
corresponding portion on the inside or below, it is still seen as
coloured.

When you have made these experiments upon the colour-
change undergone by small objects seen with outlying portions
of the retina, you will ask yourselves with astonishment how it
is that you do not always notice the differences ; that the blue
sky or the red front of a house is not surrounded by a black
border. Indeed, we should naturally expect that if a blue or
red piece of paper gradually blackens, as it is brought upon the
lateral parts of the retina, the blue of the sky and the red of the
bricks would also show some change towards the periphery of
the field of vision. And we might find considerable difficulty in
answering the question, if we had not already become acquainted
in our discussion of sensation with a large number of facts which
point out the way in which it is to be met. A sensation, we
must remember, is not anything determinate and invariable, but
the product of a comparison, or* more exactly, of its associative
relation to other sensations, which is never conditioned exclu-
sively by the character of the single excitation, but also by that
of simultaneous and preceding impressions. It does not stand
alone, but is brought into relations. If these co-operative de-
terminants are so strong as to make us, under certain circum-
stances, see blue red and red blue, — you remember the pheno-
mena of colour-contrast, — why, they may perhaps be able to
prevent our noticing the differences in colour-tone which are
produced by moving an object over the different portions of the
retina.

We have every reason to suppose that the sensations which
we get from ordinary contemplation of large and uniformly
coloured surfaces are themselves entirely uniform. For if we
move the eye, and fixate successively different portions of the
colour surface, — i.e., bring them in order upon the yellow spot, —
we receive precisely the same colour-impression in every case.
There are certainly differences given originally in sensation ; but
these we have eliminated in thousands of experiences by refer-

Development of Reflexes of Touch and Sight. 131

ring them directly to the spatial distribution of impressions,
the association being carried out with the certainty and precision
of a machine. So that when we are looking at large and con-
tinuous coloured surfaces, we simply do not notice the differ-
ences due to the place of the impression : sensation has emanci-
pated itself from them.

This fact serves to illustrate what is a universal rule in the
sphere of sense-perception, and one which we shall often have
occasion to refer to in the future. We entirely neglect a good
many of the different characteristics of a particular sensation
simply because they are not directly connected with the objec-
tive contents of the corresponding perception. If we are con-
sidering a colour as produced by some external object, we take
pains to be accurate as regards its quality. But when there is
some peculiarity in the colour-tone which has nothing to do with
the nature of the external impression, we only perceive it by the
aid of special instruments, or by an extraordinary exercise of the
attention. We can hardly doubt, therefore, that the sensation-
differences in the different regions of the cutaneous surface or of
the retina are really far greater than they appear in our ex-
periments. Prepare ourselves as we may, we still tend to notice
only those sensation-characteristics which are conditioned by
the nature of the external impression ; the mere intention to
free ourselves from a rule which has been adhered to in the
whole course of sense-development, and to which we necessarily
and unconsciously conform, does not suffice to abrogate it. We
must accordingly not content ourselves with the fact that a
peculiarity of sensation, dependent upon the position of the
portion of the sense-organ stimulated, can only be demonstrated
in the rough or in a general way. But we may certainly sup-
pose that such differences exist and are effective in cases where
the deficiency of our observational methods prevents our cogni-
tion of them. For the facts mentioned above show that the
sensation-difference must have become quite extraordinarily
large, if it is to be apprehended as a subjective difference of
sensation, and not simply referred to local differences in the
objective stimulation.

Now what is the cause of these peculiar differences in sensa-
tion ? It is plainly entirely local ; and it must, therefore, be

132 Lectures on Human and Animal Psychology

looked for in the structure of the sense-organs. Differences of
tone and colour we referred ultimately to differences in the ter-
minal organs of ear and eye. So these further qualitative differ-
ences, peculiar to the sense of sight, must be ascribed to slighter
variations in the structure or chemical constitution of the retinal
end-organs. The assumption is not by any means without
factual support. Observation shows that it is especially the
sensitivity to red light that decreases towards the periphery of
the retina. This is interesting, because the most frequent type of
partial colour-blindness, as we saw before, is red-blindness. So
that ordinary red-blindness possibly means nothing more than
an extension of the normal sensibility of the lateral parts of the
retina to the centre.

In the skin, too, there are many local differences which may
serve to explain the qualitative variation of sensation with the
place of the portion of the organ stimulated. The bulb-shaped
end-organs which take up tactual stimuli are distributed in
various quantities, like the retinal elements. There are far more
of them, e.g., at the sensitive finger-tips than in the comparatively
insensitive back or thigh. And there are further differences in
the thickness of the epidermis, and in the nerve-supply of neigh-
bouring tracts of skin, which may bring it about that one and
the same impression is differently sensed at different parts of
the surface of the body.

And now we have established a fact which may help us to
answer the question raised a little while ago. We had asked
for the conditions under which a system of reflexes at first
entirely irregular could give rise to one of regular and uniform
movements. We have found that the skin and the eye, the two
sense-organs whose stimulation is the principal incentive to
reflex movement, present structural peculiarities which imply
definite local differences in sensation. What must our inference
be, then, as regards sensation ? Evidently, the result will be
identical with that which we have when a colour is recognised
as the same colour, or a tone as the same tone. Each particular
sensation will be recognised in terms of this attribute of depend-
ence upon the place of the impression ; and we shall be able
to recognise from the attribute the locality of the sensation itself
when we have once had experience of its position.

Development of Reflexes of Touch and Sight. 133

This whole group of facts, then, leads us to a single conclu-
sion : that we have in it the principal condition of the purposive
development of the reflex. That development consists, once
more, in this, — that a movement which is at first purposeless
comes to have a definite object, the object being the sensitive
spot which was stimulated by the external impression that
released the reflex. That this spot may be discovered by the
reflex movement, it is necessary for it to be recognised in each
particular case. And just as colour and tone are only appre-
hended as like or different because their sensations are indis-
tinguishable or distinguishable, so the recognition of the locality
of an impression can only be effected by means of definite
sensation- characteristics, — characteristics which depend solely
upon that locality. We have shown that there are such charac-
teristics. And with that proof we have given the first condition
for the regularity and uniformity of the reflex : it must be looked
for in the structure of the organs themselves. At the same time
we have not yet given an altogether complete and satisfactory
account of reflex development. We find that the movements
always take the shortest and simplest road to their purpose ;
and the structure of the sense-organs cannot, of course, explain
that. It can only tell us how it is possible for the reflexes to
have a purpose, not how they can attain it. There must be a
further explanation of this, to be discovered in the movement
itself. We must, therefore, go on to ask whether any such
explanation is admissible, and what are the terms of it.

LECTURE IX

§ I. MUSCLE-SENSATIONS : THEIR INFLUENCE UPON LOCALISATION.
§ II. CONNECTION OF SENSATIONS OF MOVEMENT WITH OTHER
SENSATIONS. § III. INFLUENCE OF PRACTICE UPON REFLEX
MOVEMENTS. § IV. ARRANGEMENT IN SPACE A PROCESS OF
ASSOCIATION.

§ I

REFLEX movements become transformed from their
original purposelessness and irregularity, so that they
conform to definite ends and follow definite laws. And the
essential factor in this transformation can only be looked for in
the movements themselves. So the question arises as to our
measurement of muscular movement.

When we move the legs in walking, we measure off the length
of each step, without having to follow the movement with the
eye. The practised pianist has acquired such skill in estimating
the distances of the various keys, that his fingers scarcely go
wrong by a hair's-breadth. And we possess an accurate judg-
ment of the force of muscular movement. We discriminate the
magnitude of different weights by lifting them. (It has been
already shown that this discrimination is not made in terms of
the pressure of the weights upon the skin, but by reference to-
the act of lifting, You will remember that if lifting is allowed,
a difference of -j^ can be distinguished ; while in the case of
simple pressure upon the skin a difference of £ is only just
noticeable. Cf, above, p. 27.) So that we possess a very
accurate measure of the force and extent of movement in the
movement itself. And such a measure can have been acquired
only by aid of the sensation which accompanies muscular move-
ment. For sensations are, as we know, the only means by which
we receive intimation of changes, whether outside of us or within
our own body.

134

Muscle- sensation. 135

Now, if we attend closely to our movements, we become aware
that they are, in fact, always attended by sensations from the
muscles. As a rule, it is true, these sensations are so weak that
they escape our notice. It is only when we are exerting a
certain amount of effort, — e.g., moving a whole limb, — that we
observe with any clearness the strain-sensation in our muscles,
although much less extensive movements are capable of pro-
ducing sensations of considerable intensity, if they are frequently
repeated, and so occasion fatigue. Fatigue manifests itself by
a muscle-sensation, sometimes present while we are at rest,
sometimes only appearing (or at least only becoming actually
painful) when we move.

The fact that muscle-sensations must be unusually intensive
before they can attract our attention depends upon the ultimate
character of our sense- perception. We saw above that sensa-
tions which cannot be referred to properties of external objects
are very easily overlooked. The local colouring of the sensations
of sight and touch escapes immediate observation, because we
ordinarily direct our attention only upon the place from which
the external impression comes. In like manner, we take no
account of our muscle-sensations as sensations, but regard only
the perception whose instruments they are, the force and extent
of the movement made. The sensation calls up at once the
complex idea of which it is a constituent ; and we require special
experimental methods, or an unusual intensity of sensation, if
we are to become conscious of it as such.

The sensations which accompany muscular contraction are
probably occasioned by the pressure which the contracted
muscle exerts upon the sensory nerve- fibres contained in it.
But besides these sensations accompanying actual contraction
and the cutaneous sensations of pressure and strain which are
always connected with them, there are still other sensations
involved in movement, whether executed or merely intended.
Our sensations of movement are by no means dependent solely
upon the external or internal work performed by the muscles,
but are influenced also by the intensity of the impulse to move-
ment proceeding from the central organ in which the motor
nerves have their roots. This fact is most clearly indicated by
observations on pathological changes in muscular activity. A

136 Lectures on Human and Animal Psychology

patient who is partly paralysed in leg or arm, so that he can only
move the limb with very great effort, has a distinct sensation of
this effort : the limb seems heavier than it used to be, as though
weighted with lead ; that is to say, there is a sensation of greater
expenditure of force than before, although the work actually
done is the same or even less. For the performance of this
amount of work there is required an innervation of abnormal
intensity. In the same way, the patient will deceive himself,
especially in the first stages of the disease, with regard to the
extent of his movements. His steps are short and uncertain ;
his hand misses the objects which he is reaching for. By degrees,
if his condition remains unchanged for a long time, he regains
more or less precision of movement ; practice gives him familiar-
ity with his new system of muscle-sensations.

Sometimes this state of partial paralysis is confined to a single
muscle group, or even to an individual muscle. In the eye, e.g.,
the partial paralysis may affect merely the single muscle which
turns the eyeball outward, .and which anatomists call the ex-
ternal rectus. There then arises a very curious alteration of
vision. The patient has a wrong idea of the locality of the
objects he sees on the side of the diseased eye : he places every-
thing farther outwards than it really is. If he tries to take
anything in his hand, he reaches out beyond it. A day-labourer
whose work was stone-breaking, and who was attacked by the
disease, began to hammer the hand that held the stone instead
of the stone itself. But in these cases, too, it has always been
found that, if the condition persists unchanged, the patients
gradually become accustomed to their state, and regain the
power of accurate movement, the only abnormality being the
feeling of greater effort in the diseased part

These phenomena of partial muscular paralysis render it in-
telligible that even in cases of complete paralysis there may
still persist the idea of active movement of the paralysed muscle.
If a patient whose leg is completely paralysed makes a firm
resolve to move it, he may have a distinct sensation of muscular
strain, and consequently an idea that the leg has really moved.
By calling in the aid of sight he can, of course, convince himself
that he has been deceived : in the dark the illusion is complete.
The same thing happens when it is the eye that is the totally

Muscle-sensation. 137

paralysed organ. The idea of an actual movement is connected
with the inefficient resolution to perform that movement. The
result is an optical illusion ; external objects appear to have
moved in the direction of the purposed movement of the diseased
eye. This apparent objective movement is evidently a necessary
consequence of the subjective illusion. If the eye had really
executed the intended movement, the images cast by external
objects upon its retina could only have retained their positions
unchanged, if the objects themselves had moved in the direction
of the eye and in complete accord with it.

It has sometimes been thought that the act of will suffices of
itself to explain these subjective movement-illusions. If I will
to move an organ which is dependent upon my volition, it is
said, there is necessarily connected with my resolve the idea of
its actual movement. But it is difficult to see how a resolution
can contain in it that peculiar sensation of muscular effort by
which the magnitude of movement is measured alike in cases of
partial and complete paralysis. It is surely evident that this
sensation is a process accompanying the act of will, and capable
of varying in degree, for one and the same volition, with vari-
ation of its particular conditions. Under ordinary circumstances
the sensation is demonstrably caused by the stimulation of the
sensory nerves following the contraction of the muscle. How
can it arise in cases where the muscle is not able to contract ?

We must remember that muscle-sensations always accompany
the particular volition. Hence, whenever a volition is repeated,
the appropriate muscle-sensations will be connected with it.
And since they are familiar to us from numberless previous
perceptions, and are inseparably and invariably connected with
the will-process, they will be found along with this latter even in
cases where the muscle is unable to contract and so to furnish
the usual sense-stimulus. Now we give a special name to all
those sensations and ideas which, though not occasioned by
external, but by internal, stimuli, are yet completely dependent
for their determination upon previous external excitation : we
call them reproduced sensations and ideas. And we may accord-
ingly consider these sensations of muscular effort which are the
invariable accompaniments of volition as reproduced muscle-
sensations, while we distinguish them from others of like nature

138 Lectures on Human and Animal Psychology

by the intimacy of their connection with special processes of con-
sciousness, — volitions, — and by the constancy with which they
accompany these. They will, of course, accompany them in
cases where the influence of the will upon the muscles is
normal and effective ; but there they will at once fuse with the
actual muscle-sensations occasioned by the stimulus of con-
traction. In other words, their effects can only be separately
followed out when, as in the illustrations given above, partial
or total muscular paralysis has disturbed or entirely destroyed
the other muscle-sensations which are peripherally excited.

For any historical investigation into the development of our
sense-perceptions, the question of the origin of sensations of
muscular effort is of far less importance than the analysis of the
phenomena which are brought to light by their disturbance.
The gradual adaptation to the diseased condition in cases of
partial muscular paralysis, like those which we have noticed,
seems in particular to be at least as instructive as the condition
itself. It shows what sort of influence muscle-sensations may
have exercised upon the development of the senses. Our recog-
nition of the position of an object is normally based upon the
sensation of effort attending the movement of the sensing organ
to the object. If this power of localisation may be gained afresh
after a total transformation of the whole system of muscle-
sensations has taken place, there is not the slightest difficulty in
the hypothesis that, when sense-perception in general was in
process of development, the establishment of a relation between
muscle-sensations and the place from which an external stimulus
operates was a matter of slow and gradual growth. And this
takes us directly back to our original problem. We set out from
the proposition that, if reflex movements admit of accurate
measurement, the measure can only be looked for in the move-
ments themselves. We found the measure required in sensations
varying with the force and extent of movement. We have now
proved, by an appeal to experience, that it is by means of
these movements that our limbs and organs of touch acquire
their accuracy of function. Any alteration in the muscle-

Sensations of Movement and Other Sensations. 139

sensation does away with this accuracy. And it can only be
regained, if at all, by a fresh course of practice.

Our view of the development of reflex movements will, then,
be somewhat as follows. They owe their origin in the first
instance solely to neural connections existing within the central
organ ; that is their only primary condition. The sensation
occasioned by a stimulus gives rise to a more or less extended
movement, and this in its turn to a muscle-sensation. The
movement is, therefore, only a middle term between two sensa-
tions : between the original sensation caused by the external
stimulus and the muscle-sensation which results from the move-
ment. But there is more in the whole process than this. When
wemove our limbs, it is either that they themselves may come into
contact with the sensitive surface of the sense-organ, or that they
may transfer the stimulus from one portion of that organ to
another. Suppose that a stimulus operates upon the skin. In the
movements which are aroused this or that part of the skin is
touched; in other words, there results a second sensation of contact,
beside that already caused by the external stimulus. And this
naturally arises in the near neighbourhood of the other, since
the excitation-process which underlies sensations of moderate
intensity extends only to adjoining nerve-connections, and so
sets in movement only the contiguous muscle groups. The
total process now consists not of two, but of three, sensations.
The last two of these (sensation of movement and secondary
sensation of contact) are at first of indefinite extension. But
very soon there comes to the front some particular contact-
sensation, one which is similar in character to the sensation
which stood first in the entire series, and which was directly
occasioned by the external stimulus. And this similarity is
obviously conditioned by contact with the place upon which the
stimulus originally operated. We have seen that there attach
to every portion of the skin certain local characters, by means
of which it can be distinguished and recognised. The end of the
movement will be then the production of a sensation of contact
at the place upon which the stimulus operated. This end is
easy both of proposition and attainment. For we can recognise
not only the peculiar character of the contact-sensation, but also-
that of the muscle-sensation corresponding to it. If we suppose

140 Lectures on Human and Animal Psychology

all this to have happened in a large number of cases, we see that
a firm connection will have been established between the two
sensations. So soon as a stimulus operates, and a sensation is
aroused, the corresponding sensation of movement is awakened,
and with it the movement, which is responsible for the final
term of the whole series, — a sensation of contact identical in
local character with the sensation constituting its initial term.

In the eye we find these phenomena modified by the peculiar
structure of the organ. The nervous connections of the retina
place it in reflex relation to the muscles which move the eyeball.
One portion of the retina is characterised by an especial clear-
ness of sensation. While upon the peripheral parts different
colour-impressions are practically all sensed as the same uniform
grey, and even as they approach the centre remain for some
time indistinct in tone, upon the 'yellow spot' they are clearly
and accurately distinguished. Hence the law which governs the
development of the reflex movements of the eye : — every im-
pression, upon whatever part of the retina it fall, is brought to
the place of clearest vision, the yellow spot From the whole
series of purposeless reflex movements there comes into promin-
ence this particular one, the effect of which is to place the eye
directly in such a position, that the stimulus can act upon the
yellow spot. Here too, then, a definite movement-sensation,
whose purpose is to regulate this definite movement, becomes
connected with the local character of the retinal sensation, wher-
ever it may be aroused. And the final term in the total process
is always a sensation which is recognisable because character-
ised by its relation to the yellow spot

But while we have been describing the development of re-
flexes, as we observe it in experience, we may, perhaps, have
fallen into a grave error. We seem to have been ascribing to
the organism, at this early stage of its mental development,
definite tendencies and purposive actions. Should not the phe-
nomena under observation be rather regarded as subject only to
mechanical laws ? In other words, is it not we who are putting
purposiveness into them, while the sensing and moving subject
itself knows no more of that than the stone knows of the inten-
tion of the boy who picks it up and throws it ?

We cannot, it is true, predicate ' purpose ' and ' intention '

Sensations of Movement and Other Sensations. 141

of these elementary processes of sense-perception in the signi-
fication which the words possess for ourselves. Nor, as a
matter of fact, is anything of the kind presupposed in the above
account of them. The processes which we assumed as necessary
for the regulation of reflex movements are of just the same
nature as those present in the discrimination of sensations ac-
cording to intensity and quality. They consist in the connection
of sensations which are excited simultaneously or in immediate
succession by the operation of a sense-stimulus. Such connec-
tions are termed in general associations, and are distinguished as
simultaneous and successive. Now the unfailing characteristic of
an association between two sensations, a and b, is this : that
when one of them, a, is given, b is added to it, even though the
external stimulus for b is not present. In other words, the cri-
terion of an association is the spontaneous reproduction of one
of the members of an association complex. Taking this criterion
as our guide, and carefully observing the facts, we find that the
association between definite sensations becomes stable in pro-
portion to the frequency of its repetition. But besides frequency
of repetition, which is involved in all the phenomena of practice
and habituation, there is a second influence of importance at
work in this particular case. If a sensation, a, enters into two
associations, one with a similar or related sensation, b, and one
with a quite different sensation, c, the resulting complexes
possess a different character. In the association a + b, the com-
ponents are apprehended as similar and associated ; in the
association a + c, as dissimilar and associated. So that all
associations of sensations may be divided, again, into associa-
tions of similar and associations of dissimilar sensations. Two
musical clangs, e.g., which constitute a harmonic interval, form
a similarity-association ; they are related, as we have seen, by
certain common partial tones. But two completely different
sound-impressions, which have no elements in common, form an
association of dissimilar sensations. If now a sensation, a, has
become associated with several other sensations, b, c, d...t of
which b is more like it than c, d... are, the similarity-association
has the advantage, other things equal : it forms more readily
than the alternative associations. This is not difficult to ex-
plain. The transition from a to b will be facilitated by the

142 Lectures on H2iman and Animal Psychology

existence of properties common to both ; b is partly contained
in a, and so is already partly present when a is present.

Apply these considerations to the phenomena which we have
been examining. It is at once clear that they can all be ex-
plained as association-processes. Light-sensations, e.g., form
associations with the corresponding sensations of the ocular
muscles. And these have become so stable, owing to the func-
tional connection of light-impressions with the resultant reflex
movements, that even if actual movement is prevented, the
reproduced sensation of movement is still present. Or, again,
the relation of light-impressions in the visual field to the spot
of clearest vision is a characteristic instance of the association of
similar sensations. This association, being preferred to all the
other possible ones, is, of course, rendered still more stable by
continual repetition. So that if in describing the development
of these reflex connections just now we chanced to speak of the
' recognition ' of an impression, of its ' being brought upon '
the spot of clearest vision, that must not be interpreted to imply
that deliberation and reflection are at work, in the general sig-
nification of these terms. It was necessary, in order to be
intelligible, to translate certain processes of what we may call
mental mechanics, — certain association-processes, — into the lan-
guage of logical thought. Logical thinking is the form of mental
activity with which we first become directly acquainted in our
internal experience. And so it offers a ready means of making
clear the connection of separate elements in a mental process,
although the process itself may not belong at all to the sphere
of logical reflection. But we must be careful. The logical
formulae which we often find so useful in explaining the con-
nection of mental processes must not be confused with the pro-
cesses themselves. These associations, into which the processes
of sense-perception may be analysed, form the basis upon
which all the higher mental activities, including logical thinking,
rest. It is always possible to put this farther back, to find it
in the elementary processes ; or, as it might, perhaps, be better
stated, it is always possible to translate the results of the mental
association-mechanics into the language of logical reflection, of
which it itself is wholly ignorant.

Influence of Practice upon Reflex Movements. 143

§ HI

The mental associations which we have been discussing are
of a very simple kind. And the parallel connections of phy-
sical processes are also of a comparatively simple nature. It is
not at all difficult to represent the entire complex, which we
have been looking at from the psychical point of view, in purely
physiological terms. In attempting this, we may, of course,
leave entirely out of account the sensations which accompany
the stimulation-processes in the organs of sense and of move-
ment. It is true that we are obliged at times to interpolate
hypothetical links in the chain of known facts. But these cor-
respond well enough to familiar physical laws for us to be fairly
certain that our physiological picture of the functions of sense,
determined by the scheme of the reflex process, approximates
pretty closely to the truth.

For our present purpose we may regard the general process of
stimulation in sensory nerves as some kind of movement. Of
the real nature of this movement we know nothing. We will,
therefore, not seek to define it ; we will only assume that it
obeys the universal laws of mechanics. This movement is pro-
pagated, as we saw, through nerve-cells to the fibres of the
motor nerves ; it excites a greater or less number of fibres
according to the intensity of stimulus and the degree of sensi-
bility. The weakest stimuli are confined within the particular
nerve-channel which is most directly connected with the stimu-
lated sensory nerve ; stronger stimuli have more diffused effects.
It follows that the reflex process which is set up by the stimu-
lation of a definite sensory nerve is, in the great majority of
cases, kept within one definite nerve-channel. That channel
will always be employed when reflex activity is awakened ;
whilst it will only happen occasionally that other channels are
occupied. It is an obvious conjecture that this preferential
nerve-channel is the one by which a movement is conducted
to the stimulated part ; that is, that the uniform sequence of
events in the reflex is given with the uniform arrangement of its
nervous connections. Indeed, this hypothesis may be looked
upon as exceedingly probable. Wherever the mind interferes
in the series of bodily processes, we find the conditions of its

144 Lectures on Hitman and Animal Psychology

action given in the bodily organisation. Locomotion is deter-
mined by the structure of the skeleton and the arrangement of
the skeletal muscles, sensation by the character of the nerve-
endings in the sense-organs.

Now it is a fact of common observation in external nature that
a movement which takes place again and again in the same
direction comes by degrees to follow this direction more readily
than any other, and will presently be unaffected by influences
which at first would have had no difficulty in diverting it.
When water is poured upon the ground, it forms a channel for
itself. Its initial direction may have been determined by the
merest accident ; but, once determined, is adhered to, and the
more certainly the oftener we pour. When a machine is set in
motion, there is always the same resistance of mass to be over-
come in its various parts ; but friction is lessened by the wearing
and smoothing of part against part : so that a machine which
has been going for some time usually runs more easily than a
new one, or one which has lain for a long time unused. If you
let your watch run down, and do not wind it up for a fortnight,
you know that it is always liable to stop until it has been going
again for a week or so. Now there is good evidence for the
view that the same thing holds of neural processes. If we are
in the habit of executing some definite muscular movement, we
know that it gradually becomes easier, i.e., can be made with less
expenditure of force. What we call ' practice ' consists simply
in changes of this sort. The execution of a practised movement
becomes easier because the stimulation-process in nerve and
muscle is the more easily set up the more frequently it is re-
peated. This process is originated by an increased supply of
the elements essential to the tissues ; so that exercised muscles
show an increase in the mass of their contractile substance.

Observation of purposive practice puts it beyond all doubt
that this restriction of innervation to a definite channel is a
matter of very common occurrence. Most persons are unable
to move certain fingers, — the third and fourth, — separately. But
a little practice enables one to move either finger independently
of the other. At first it requires a very considerable effort to do
this ; but, as practice is continued, the separate movement be-
comes so easy that it takes place almost of itself.

Arrangement in Space an Association 145

The course of practice in cases like these is approximately as
follows. The first time that we attempt to move the particular
muscle by itself, we are not entirely successful. However great
the effort, adjoining muscle-groups are also involved in the
movement made. With continued practice, however, this attend-
ant movement becomes weaker and weaker, and finally ceases
altogether. The uniform tendency in practice, then, is this : a
larger and larger amount of the total excitation follows the
channel of the nerve connected with the particular muscle, until,
when the process has been often enough repeated, the whole of
the excitation is confined to this single nerve-path. And that is
precisely what we observe in the development of the constant
reflexes. The only difference is, that in the present case this
transmission of the major portion of the excitation by the par-
ticular nerve-channel is a matter of volition and intention, while
in the reflexes it comes about of itself, through the connection
of sensory and motor fibres. Moreover, it is obvious that in the
present case as well it is really not will, but a frequent repetition
of the same physical processes in the nerves, which directly pro-
duces the effects of practice. If it were will, we should expect
the desired isolation of the movement to be attained at once ;
whereas, in fact, however great the effort of will, practice is in-
dispensable. On the other hand, when once isolation has been
accomplished, it is not always necessary that the will should
intervene for the production of the isolated movement.

§ IV

We have arrived, then, by different roads, at a single result.
First of all we considered the development of purposive reflexes
as a mental process. Its end proved to be the uniform limita-
tion of reflex movements. Secondly, we attempted to analyse
the process in physical terms. And here we are confronted with
the same limitation as the result of physiological practice. So
that the two investigations together, the psychological and the
physiological, furnish a concrete illustration of the principle
which we have already found to be universally valid in the
sphere of simple sensation-processes, — the principle of psycho-
physical parallelism. But we must now return to our psycholo-
gical problem, and ask : what becomes of the reflex movements

L

146 Lectures on Human and Animal Psychology

after they have been uniformly limited in the manner described ?
What influence have the associations which have arisen by way
of the reflex upon the further development of mental processes ?

We will attempt, first of all, to answer this question with refer-
ence to the eye, because the mechanism of movement is there
obviously the more simple. Eye-movements are from the first
confined to the few muscles which turn the eyeball. And the
very special sensibility of the yellow spot brings them into a
definite relation to this part of the retina. In the skin, on the
contrary, there are numerous tracts of equal importance for sensa-
tion ; or, in other words, what is given only once in the eye is
here repeated many times over.

The reflex movements of the eyeball are, as we saw, so dis-
posed that any light-stimulus, wherever in the field of vision it
may appear, is carried towards the yellow spot, the place of
clearest vision. Every light-sensation occasions a movement,
which transmits the stimulus by the shortest possible road to
the yellow spot, and with which the corresponding sensation of
movement is indissolubly connected. Another result of the
movement is to change the local colouring of the primary sensa-
tion ; this takes on the quality peculiar to the place of clearest
vision. The more remote from the centre the original stimula-
tion, the greater the modification of the sensation. Now the in-
tensity of the movement-sensation is also proportional to this
remoteness. If I lift a weight two feet, I have a more intense
sensation than if I lifted it only half as high. All our sensations
of movement are intensively graduated in proportion to the
magnitude of the movement made. The qualitative alteration
of the light-sensations, therefore, runs parallel throughout to
an intensive modification of the sensations of ocular movement.
We recognise the relation of a particular light-stimulus to the spot
of clearest vision by the local colouring which it takes on ; and
we measure this relation quantitatively in terms of the result-
ing movement-sensation. When a stationary light-stimulus is
brought upon the different portions of the retina by a movement
of the eye, the character of the aroused sensation varies from
point to point. And every such variation is paralleled by a
movement-sensation. And so we associate this sensation of
movement in the most intimate fashion with the variation, sepa-

Arrangement in Space art Association 147

rating the subjective sensation-differences from those which are
due to the action of an objective stimulus. This does not mean
that we apprehend them as subjective, that we distinguish them
as something in us from the things outside of us : there can
plainly be no question of any such distinction in these processes
of perception, entirely dependent as they are upon the mental
mechanics of association. Rather are these mental processes of
wh''ch we are treating the material from which the subject-
object distinction is gradually built up. They are but the first
step on the road to the conscious discrimination of the self. On
the other hand, there is no doubt that even at this stage a well-
defined distinction exists : the subjective differences form one
group of sensation-qualities, the other characters of sensation
another and a quite different one. And this is the fact which con-
cerns us here. A series of constantly recurring sensation-differ-
ences is brought into a relation of dependence with an entirely
similar series of sensations of movement. At the same time, in
saying this we postulate one condition the actual presence of
which might be doubted, — the condition that when once the eye
has brought an impression upon the yellow spot it leaves it again
and turns to another ; thereby, perhaps, bringing the original
one back to the particular portion of the retina which it had
stimulated in the first instance. (That must needs be the case,
if it is to be possible for us to recognise at all that a visual sen-
sation has remained unchanged.) Now there can be no doubt
that the adult human being can move his eye hither and thither,
to this point and that. He takes in any number of impressions,
one after the other, just as he pleases. But can the same thing
be assumed for that earlier stage of development at which the
simple reflex mechanism is still undethroned ? As a matter of
fact, there is one influence already at work there which render?
this variation of fixation possible, and without whose prepara-
tory operation the possibility of voluntary variation would cer-
tainly never have been realised. I mean the influence of
fatigue ; — the weakening of light-sensation after long-continued
operation of external stimulus.

Every stimulus which acts upon the peripheral portions of the
retina arouses a reflex movement, which brings its image upon
the place of clearest vision. There the impression is retained

148 Lectures on Human and Animal Psychology

for some little time, — until fatigue sets in and relaxes the mecha-
nism. After this some other peripheral impression of a different
kind, for which the retina is still unexhausted, may become the
centre of interest, and arouse a second reflex movement corre-
sponding to it. In this way you can see how a large number of
external impressions may be successively apprehended at the
spot of clearest vision. First of all will always come the most
intensive, or that whose place of stimulation stands in the
closest reflex connection with the yellow spot ; the others will
follow in definite order. Now suppose that there are presented
to the eye two luminous points at some distance from one
another. Even if the external impressions are perfectly
similar, the sensations which they excite will be possessed of
a different local colouring. If the eye moves from its original
position to another, in which the second luminous point falls
upon the place previously stimulated by the first, the second
sensation is made qualitatively identical with the first, while the
latter has changed. The sensation of movement is there to mea-
sure the distance traversed ; that is, the distance of the two
luminous points from one another.

Every particular connection of a sensation of movement with
the corresponding series of local sensation-colourings is a long-
practised association. The number of such associations is very
great ; and they enter again into associative connections with
each other. The sensations of movement forming a quantita-
tively graduated series, and the local sensation-differences being
qualitatively graduated, there arises at the same time a com-
plete parallelism of the two associatively related sensation-series.
And the result of this compound association-process ? We must
anticipate a little to state it. Since this process connects to-
gether the whole number of sensations excited in and round the
eye, it will also systematise those sensory processes which begin
with the simple light-sensation ; it will determine the form in
which the eye transforms its sensations into perception.

This form is space-perception. So that our observations, even
at this stage, lead us to the conclusion that the perception of
space, psychologically regarded, is not an innate possession of
the mind, but the product of an association of sensations. It
will now be our task to test this conclusion in detail by investi-
gating the properties of spatial perception.

LECTURE X

§ i. INFLUENCE OF OCULAR MOVEMENT ON SPATIAL VISION. § 2.
GEOMETRICAL OPTICAL ILLUSIONS. § 3. SPATIAL PERCEPTIONS
OF THE SENSE OF TOUCH. § 4. ACCIDENTAL AND CONGENITAL
BLINDNESS. § 5. WHY ARE NOT VISUAL OBJECTS INVERTED?
§ 6. CONCLUDING REMARKS UPON THE THEORY OF SPACE-CON-
STRUCTION.

ALL our previous considerations have been based upon em-
pirical facts. The laws of reflex movement, the muscular
sensibility, the local differences in sensations of light and touch,
the exhaustion consequent upon long exposure to sense-stimu-
lus, — all these are phenomena which may be verified in experi-
ence. But at the conclusion of these considerations we seem to
have left the firm ground of experience far behind us. We have
ventured upon a psychological construction of space, from the
associative co-operation of the specified factors. Is that not more
than experience can ever achieve ? Is not space a connate pos-
session of the mind ? Or, if not that, is it not at least an en-
tirely new element in our knowledge, which is sui generis, and
therefore not a derivative from anything else ?

It is certainly true that the perception of space is a new ele-
ment in our knowledge. But in this sense every psychological
fact is new which arises from some particular combination of the
elements of our mental life. The laws of this composition are
such that the properties of the mental resultants to which they
give rise can never be predicted from the properties of the ele-
ments which enter into them, although we are afterwards able to
see the connection of these elements and their combinations in
the complex result. Thus, e.g., after we have completed a com-
plicated process of inference, we recognise that the conclusion
follows necessarily from the premises. But still it is, as con-

150 Lectures on Human and Animal Psychology

trasted with the premises, something new, something which had
to be deduced by definite acts of thought. Nothing at all is
gained by such general assertions as that the perception of
space is a connate possession of the mind, or that spatial quality
is an original property of our sensations of sight and touch.
Not only are these statements not capable of proof, but those
who formulated them have not even taken the trouble of exa-
mining the psychological problem before them. For a problem it
surely remains — to ascertain whether the laws of the movement
of the eye and the organ of touch, and the sensational associa-
tions connected therewith, exert any influence upon the percep-
tions of these senses.

It is a well-known fact that we are able to compare distances
fairly accurately by means of the eyes. But it frequently
happens that two distances which are not exactly equal are
nevertheless regarded as such, just as in the case of simple
sensations the perception of a difference only becomes clear
when it has attained a certain magnitude, determined in each
particular case by the character of the sense involved. Now
in the present instance, just as in the sphere of sensation -
intensity, we can determine by measurement how great the
difference between two magnitudes must be for it to become
just perceptible.

We draw two horizontal lines of equal or almost equal length,
and ask an observer who knows nothing of their objective
relations to say whether they appear to him equal or not. If
we begin by taking the two lines equal, and gradually lengthen
one of them, we shall reach a point where the longer line is
perceived to be just noticeably greater than the other. Here
the experiment is interrupted, and the difference between the
two lines measured. If this procedure is repeated for various
lengths, we obtain a series of different values which tell us how
the apprehension of differences of distance varies with the
gradual increase of the distances compared.

The experiment is therefore essentially the same as that
which we made earlier to determine the dependency of sensa-
tion upon stimulus. We have only substituted space-magnitude
for stimulus-magnitude. If the two lines with which we begin
are one decimetre long, and if we gradually increase one of

Influence of Ocular Movement on Spatial Vision 151

them, the difference is noticed when the increment amounts to
about -g^j- decimetre, or 2 millimetres. But if the distance
with which we set out is only \ decimetre, the just noticeable
difference will be correspondingly smaller ; it will now be found
to be TJ-J^J- decimetre, or one millimetre. And this ratio remains
constant whatever other standards of measurement we may
apply. Within certain upper and lower limits the difference is
always approximately -^ of the total distance with which we
are dealing. Of the two horizontal lines in Fig. 18 the left
is 26 and the right 25
millimetres long. We

see at once that the FIG. 18.

former is the longer ;

but if it is made just a little shorter, the difference is no longer
noticed. You may convince yourselves by experiment that if
the lines are drawn twice or three times as long, their differ-
ences must also be two or three times as large.

It is at once obvious that we have here the same law which
we found to hold for the dependency of the just noticeable
sensation-difference upon stimulus-difference. The just notice-
able increment of spatial distance always bears the same ratio to
the total distance. And it is plain that this coincidence may be
explained most simply by reference to the fact that we possess
in sensation a measure for the perception of spatial relations ;
and that the sensations which give us this measure most directly
are those resulting from the movements of the eyeball, the
intensity of which must increase with the length of the path
along which the eye travels.

We hold before the face a box, ss (Fig. 19), open on one side
and having a horizontal slit upon the opposite side, through
which both eyes can look towards a white screen, w, and see it
without perceiving any of the other objects in the room. Now
we hang between the screen and the eye a vertical thread,/",
kept taut by a weight. Each eye will of itself take up such a
position that the thread f forms an image at the yellow spot,
the place of clearest vision. The line drawn in space from this
point through the centre of the eye is called the visual axis
We may say, therefore, that the visual axes of the two eyes cut
one another or intersect in / If we now alter the position of.

152 Lectures on Human and Animal Psychology

the thread somewhat, by bringing it nearer or removing it
farther from the eyes, the angle formed by the intersection of
the visual axes is changed at the same time ; for the eyes
always follow the thread and remain directed upon it. If the
thread is removed to a greater distance, both eyes turn out-
wards, and the angle of intersection becomes more acute ; if
the thread is brought nearer, the eyes turn inwards, and the
angle of intersection becomes more obtuse. When we know

• 'he alteration in the distance of the

w

thread, we can easily determine how

far each eye has turned round its
centre. If the thread is moved little
by little, the alterations in its distance
will not be perceived at all ; i.e., the
turning of the eyes round their centre
is so slight that the accompanying
movement-sensation is ,not notice-
able. This sensation of movement
* 1G- W- only makes its appearance when the

alteration in the position of the thread has reached a certain
magnitude ; and then we perceive that the thread has been
brought nearer or removed farther off. This limiting point
must be determined in a long series of experiments, and with
different distances of the thread from the eye. We should find
that the eye possesses the finest sensibility for its own move-
ments when the two visual axes are practically parallel, i.e.,
when the eyes are approximately in their position of rest.
Under th :>se conditions we can perceive an alteration of distance
if the revolution of each eye round its centre amounts only to
about the sixtieth part of an angular degree, or to i'.

But so soon as the eyes have turned inwards to any con-
siderable distance, — which happens, of course, when the thread
is brought nearer, — the just perceptible movement is very much
larger. And we shall find that the magnitude of this just
noticeable movement increases in direct proportion to the dis-
tance of the eye from its position of rest.

We are plainly here only dealing with a further confirmation
of the universal law of the dependency of just noticeable
sensation upon stimulus. The turning of the eye inwards

Influence of Ocular Movement on Spatial Vision 153

brings about a definite sensation of movement. The magni-
tude of the movement corresponds to the intensity of the
stimulus ; the greater the movement already present, — i.e., the
greater the stimulus already operative, — the greater must be the
increase of movement or the increment of stimulus. And if the
apprehension of sensations of movement follows the same law
as that of the sensations of the external senses, it is to be ex-
pected that the increment of movement corresponding to the
equally noticeable increment of sensation will always bear the
same ratio to the total movement already present. As a
matter of fact, experiment proves that this relation is approxi-
mately constant. Even such deviations as occur correspond to
the rule which we have found to hold in the case of sensations
of the external senses : that is, when the extent of the move-
ment is very great, the fineness of discrimination becomes
somewhat less than we should expect it to be according to the
law. But the increment of movement which just suffices to
produce a noticeable sensation amounts approximately to
-g^- of the total movement-magnitude. This result is in
complete accord with what we have already obtained from the
comparison of spatial magnitudes : a longer line can be just
distinguished from a shorter when the difference between them
amounts to -^ of the length of the latter. But if the
perception of a spatial distance is directly proportional to the
effort of movement made by the eye in traversing this distance,
we must conclude that the effort of movement is the criterion
of perception. And since we can only have know-
ledge of the effort through the movement-sensation,
the influence of the latter is also demonstrated.

These experiments on the connection of the
sensation of movement with the estimation of dis-
tance may be supplemented by the following observa-
tion. We suspend two black threads, side by side
and parallel to one another, at a little distance
from a bright background, and fixate them with one
eye (Fig. 20). We then move gradually away from

them, keeping; them constantly fixated as we move.

FIG. 20.
Since distant objects look smaller than near ones,

the apparent distance between the threads continually decreases,

154 Lectures on ffiiman and Animal Psychology

until a point is reached where the two appear as one. Now
the decrease in the size of an object as we move away from
it is due to decrease of the magnitude of its image upon
our retina. So that the experiment shows that there is
a certain magnitude of the retinal image of two points
below which they cannot be perceived as separate. This
magnitude of the retinal image (b) or of the corresponding
visual angle (w) may be determined, since the distance between
the threads and their remoteness from the eye are known. We
find that the two images fuse to one at the moment when the
distance between their retinal images has become so small that
the eye has to turn only about i' in order to bring first
one thread and then the other upon the same point of the
retina. But that is the same magnitude as we discovered above
to be that of the just perceptible movement of the eyeball. It
follows, therefore, that the resting eye apprehends the distances
of objects in space with the same degree of accuracy as that
with which it apprehends its own movements under the most
favourable conditions, i.e., when the movement begins with
the visual axes parallel. The limit which it can attain to in
the cognition of spatial distance is identical with the limit
set to its apprehension of the sensations of its own move-
ments.

The dependency of spatial apprehension upon sensations of
movement, which we have inferred from these fundamental
experiments, is confirmed by many other of the phenomena of
vision. The muscles of the eye are on the whole symmetrically
arranged. Thus one muscle (a\ the rectus externus, turns the
eye outwards, and another (b), the rectus internus, turns it inwards
(Fig. 21). The two muscles differ but little in their dimensions,
and both lie in a horizontal plane, which passes through the
centre of the eyeball. Their position is, therefore, the most
advantageous possible for the movements which they are to
bring about. This complete similarity of conditions renders it
obvious that sensations of movement occasioned by equally
extensive revolutions will be of approximately equal intensity,
whether these revolutions be made inwards or outwards. We
find the same correspondence as regards movement upwards and
downwards. The eye is chiefly moved upwards by means of a

Influence of Ocular Movement on Spatial Vision 155

FIG. 21.

single muscle (c}, the rectus superior,
which runs obliquely forwards in the
upper part of the socket of the eye, and
is affixed to the upper part of the eye-
ball, a little outwards from the middle.
Its action is assisted by the operation
of another muscle, which is hidden by
the eyeball in our figure. This muscle,
the obliquus inferior, runs in the lower
portion of the socket, from before and
within backwards and outwards, con-
necting with the posterior surface of
the eyeball. Equally symmetrical in
their arrangement are the muscles by which the downward
movements are mediated. The operation of the muscle lying
opposite to c on the lower side of the eyeball, the rectus
inferior, is aided by a muscle, d, the obliquus superior, which
runs forwards and inwards, and pulls on the upper surface
of the eyeball. Owing again to the symmetrical distribu-
tion of the muscles, the effort of movement is approximately
the same whether we turn the eye up or down. On the ether
hand, there is a very considerable difference between the ar-
rangement of the muscles which turn the eye outwards or
inwards, and that of the muscles which turn it up or down. If
similarity were required in this relation also, the muscles would
have to be so placed that the rectus superior (c), which moves
the eye upwards, and the rectus inferior, on the other side of the
eyeball, which moves it downwards, should be inserted at the
point where they would best subserve the movement which they
are to effect. This is, however, as our figure shows, not actually
the case. The direction of c is somewhat more oblique than
that of a and b. With an equal expenditure of effort, then, the
former muscle would move the eye a less distance upwards than
either one of the latter pair would turn it in or outwards. For
this reason it is assisted by a second muscle. So that the effort
necessary to produce a movement up or down is in general
greater than that required for an equally extensive movement
outwards or inwards, and, accordingly, the movement-sensations
are more intensive ; and we must expect to find that distance in

a vertical direction will appear greater than the same distance
in a horizontal direction. This is true as a matter of fact. If
we draw a cross with equal arms, it will appear
longer in the vertical direction (Fig. 22) ; while
in other figures, such as squares or rectangles, the
vertical distances are similarly overestimated.

§ n
FIG. 22.

These differences in the estimation of vertical

and horizontal distances are the most important, but they are
not the only errors made in measurements by the eye. Smaller
differences of a similar character may be observed between the
upper and lower half of a vertical line, and between the inner
and outer portions of a horizontal line. So that, strictly speak-
ing, no one of the four arms of the cross in Fig. 22 appears
exactly equal to any other. These lesser differences also corre-
spond in every case to asymmetry in the arrangement of the
muscles. When we remarked above that the two muscles a and
b, which move the eye out and in, differ but little in their
dimensions, it was, of course, implied that they are not completely
similar. As a matter of fact, b, the rectus interior, is somewhat
more strongly developed than a, probably because the converg-
ing movements of the visual axes predominate in all cases
where we are occupied with what is near at hand, — i.e., are fixat-
ing near objects : so that b is exercised more than a. It may
be observed, accordingly, that the external half of an exactly
bisected horizontal line appears longer than the inner half ; the
weaker muscle requires a stronger effort to produce a like move-
ment, and the greater effort is accompanied by a more intensive
muscle-sensation. To realise this apparent inequality, it is, of
course, necessary to close one eye. For the outside for the
right eye is the inside for the left ; binocular vision destroys the
inequality. A similar difference, and one which does not dis-
appear in binocular vision, is that between the upper and lower
half of the field of vision. If we look closely at the cross in
Fig 22, we see that the upper half of the vertical line appears
somewhat longer than the lower. And to this difference, again,
there corresponds an asymmetry of muscular distribution. The
muscles which pull the eye down are more strongly developed

Geometrical Optical Illusions 157

than those which move it up, — probably for the same reason
which we found to hold in the case of the internal and external
recti. Since the visual axes are usually directed somewhat
downwards, — and this is especially true when we are fixating
near objects, — the muscles which move the eye below the horizon
get the more exercise, and an upward movement consequently
involves a greater strain than an equally extensive movement
downwards.

These visual effects of asymmetrical muscular distribution on
the eyeball allow us accurately to predict other anomalies in the
estimation of distances, which can be experimentally demon-
strated. You know that we are more tired if we walk, a distance
in many short steps than if we take longer and fewer ones. The
same holds of the eye. In passing over an uninterrupted path,
it moves with less effort than over an equal distance which is
frequently subdivided. If we bisect a straight line, then, and
divide up one half into numerous smaller sections, the sub-
divided portion appears considerably longer than the other
This experiment may, of course, be varied in all manner of ways.
A subdivided angle appears larger than the same angle when
open ; a plane figure appears larger when divided up into numer-
ous smaller areas than one which is objectively equal to it, but left
undivided, etc. These phenomena, which can be best observed
in geometrical figures, have been designated geometrical optical
illusions. They are all convincing proofs of the co-operation of
sensations of ocular movement in the act of spatial vision.

*

§ III

The spatial perceptions of the sense of touch differ in many
respects from those of the sense of sight. The difference may
be partly due to the fact that in the normal development of
our mental life the eye ranks as a far more perfect instrument
than the skin, and that its particular development appears to
precede that of the more delicate perceptions of the sense of
touch. This does not mean, of course, that the two processes
are sharply separated ; they rather cross one other, each in-
fluencing and assisting the other. But at least for man and
the higher animals vision is the earlier activity, so that ihe sense

158 Lectures on Human and Animal Psychology

of touch is rather guided and educated by sight than vice
versa.

If we remember that the pressure-sensations of the skin are
always influenced by vision, we shall see that the local relations
which attach to them must be primarily visual. But the sensations
of touch are of such a character as to be able to throw off this
influence to a certain extent. For the skin, as for the eye, the
peculiar property of sensation which depends upon the locality
of impression varies from place to place. So that this locality
may in time be recognised by the local colouring of the sensa-
tion itself, without its being necessary to call in the eye to assist
in the determination. When once the eye has settled the relation
of the locality to its local colouring, we are able to refer a
definite sensation to its right place upon the cutaneous sensitive
surface.

It follows from this that the spatial discrimination of im-
pressions will no longer depend upon movements, or upon the
vividness and comparability of their accompanying sensations,
but simply and solely upon the greater or less difference in the
local colouring of sensations. If two contiguous portions of the
skin differ indefinitely little in this respect, we shall not be able
to distinguish the sensations proceeding from them. We shall
only apprehend the impressions as spatially different when they
affect portions of the skin whose sensational character is really
different. And it is plain that this limit is not a fixed and un-
changeable one, but that by close attention to our sensations
we shall become able to distinguish between impressions lying
nearer and nearer together. It is in this way that the great
influence of practice observable in experiments of this kind finds
its natural explanation.

In the same manner, the differences in power of discrimination,
which we find existing at various points on the surface of the
skin, will depend on the fineness with which the local sensation-
differences are graduated. These divergences are really very
large. On the finger-tips we can plainly distinguish as separate
two impressions, e.g., two compass points, the distance between
which is only one millimetre ; while upon the skin of the back
the distance must be 60 millimetres. So that the entire skin
may be regarded as a graduated system of sensitive points

Spatial Perceptions of the Sense of Touch. 159

But these points are not arranged uniformly upon it in order of
sensitivity, but are at various distances from each other, and
variously distributed. Besides the natural character of the
cutaneous sensations, their control by the eye may contribute
somewhat to this graduation. Not all portions of the skin are
equally subject to visual control ; many, like the skin of the
back, lie entirely beyond it : others, such as the hand and
fingers, are peculiarly subject to it. It must also be remembered
that all portions of the skin do not naturally get a like
amount of practice. It is again the hands, and especially the
tips of the fingers, which are most constantly exercised ; and
after them come the lips and tongue. On account of this
natural difference in amount of practice, the further develop-
ment of the spatial discrimination of the skin, which we attain
to by voluntary practice, differs considerably for different parts
of the organ. On the finger-tips, e.g., it is quite small, on the
upper and lower arm strikingly large ; the power of discrimina-
tion may be doubled or even quadrupled in the space of a few
hours. The advantage of such practice, it is true, quickly dis-
appears : after twenty-four hours it has perceptibly decreased ;
after a few weeks or months it has entirely vanished. But the
result is not limited to the portion of the skin directly exercised.
If, e.g.y the fineness of apprehension has been doubled on the
back of the right hand, the sensibility of the left will have in-
creased by an equal amount, although that hand has not been
exercised at all. The same result is obtained from all sym-
metrical portions of the skin. At the same time, the effects of
practice never extend beyond these symmetrical portions. By
practising the right lower arm or right cheek, we cannot help
practising at the same time the left lower arm and the left
cheek ; but there is no practice of the upper arm, or breast, or
forehead. This peculiar result must be explained by reference
to the psychological processes involved in practice. In practis-
ing, we learn to attend to sensation-differences which before
escaped our notice. Now the local character of sensations of
symmetrical portions of the skin is very similar. If, therefore,
we have learned to attend to smaller sensation-differences upon
the one side, we shall also have learned to do the same for the
corresponding differences on the other. Especially with respect

160 Lectures on Hitman and Animal Psychology

to right and left, there is complete correspondence in fineness of
graduation and in the rapidity with which the local colouring
alters from point to point. The case is, of course, different
when we are dealing with asymmetrical places ; the sensations
and their gradations are so different, that experience gained at
one place can never be applied to another. Or at most, this
previous knowledge can only be valuable because the attention
in general has been rendered more keen by practice.

We have seen that the smallest noticeable difference on the
skin is probably not determined by reference to sensations of
movement at all in the case of the normal seeing individual, but
is simply the result of the discrimination of local sensation-
differences. In the same way, our judgment of the increase or
decrease of the spatial distance between impressions of touch
will depend solely upon the knowledge which we possess of the
position of each impression in terms of the local colouring of its
sensation, or, more correctly, upon the permanent associations
into which the two are brought. But this knowledge was
acquired with the assistance of the sense of sight. We judge
whether a distance on the skin is longer or shorter from the
memorial image of the position of the stimulated part which its
sensation arouses in us. This memorial image is independent
of the movement required to pass over the distance ; it is con-
ditioned solely by the idea which the sense of sight has helped
us to form of every portion of the skin as determined by its
peculiar sensational character. And it is an obvious inference
that the discrimination of spatial distances, whether large or
small, always remains unchanged so long as the sensibility of
the cutaneous surface itself remains the same. This is the result
which we actually obtain by experiment. If a distance of 1 1
millimetres is just noticeably different from one of 10 milli-
metres, we can also distinguish 21 from 20, and 31 from
30 ; in short, for cutaneous sensibility in general, it is not the
relative, but the absolute, just noticeable difference of distance
which is constant. Exceptions to this rule are explicable from
the fact that in long distances the fineness of our discrimination
of neighbouring cutaneous points is considerably altered.

Accidental and Congenital Blindness 161

§ IV

The normal development of the sense of touch, then, comes
later than that of the sense of sight ; so that the measure which
it applies to space is obtained from visual perceptions, and not
at all or only secondarily from sensations of movement in the
limbs. For this reason the mechanism of the touch reflexes and
the laws of its development will not possess the great importance
which attaches to them in the development of vision. Their
influence must necessarily be diminished to the extent, that is,
to which it is destroyed by the predominance of the sense of
sight.

But this destruction is only partial. Every influence which
makes against that of the sense of sight increases the independ-
ence of touch, and helps to develope it to an extent which is
never attained under ordinary conditions. Accidental blindness
shows us striking alterations in this respect : the muscles become
much more responsive ; the least tactual stimulus arouses move-
ments which bring the external object into contact with different
parts of the skin, and particularly with the most sensitive portions.
And much greater still is the part played by tactual movements
in those rare instances where the dominant influence of the
sense of sight has been absent from the very beginning of mental
development, — in cases of congenital blindness.

The congenitally blind are forced to construct their entire
spatial world from the perceptions of the sense of touch. And
they do this with marvellous completeness. That sense which
remains throughout the normal life on a low plane of develop-
ment attains a perfection which in fineness of discrimination
may at least be compared with that of indirect vision, the vision
of the lateral portions of the retina. In one respect only must
the skin necessarily remain inferior to the eye : it requires im-
mediate contact with its impressions.

How now will the congenitally blind acquire ideas of distance
in space or of spatially extended objects ? They have at their
disposal simply pressure-sensations from the skin, and sensations
of movement from the exploring limbs. From these alone they
must construct their perceptions of space. The means to this
construction is obviously to be found, as it is in visual perception,

M

1 62 Lectures on Human and Animal Psychology

in the association of the two sensational series by the uniform
working of the reflex mechanism. But of course this latter
requires a much more complete development in the blind than
in the seeing. First of all, each limb is brought into reflex con-
nection with some definite portion of the skin. The local differ-
ences of sensation are in consequence associated with definite
sensations of movement ; so that there exists for each of these
provinces of the skin some central point (although this may per-
haps be variable) to which all neighbouring sensations are referred.
Then, further, the separate portions of the skin are brought into
relation with one another ; and so, by the interconnection of
originally diverse sensational systems, the whole mass of cuta-
neous sensations is united into a single system. This inter-
connection must necessarily tend to be effected whenever the
separate limbs come into contact with one another. For in this
way there will be obtained a certain measure, however imperfect,
of the distance between the separate organs of touch and their
sensation-centres.

The course of this development will undoubtedly require a
longer time than the education of the visual sense. The latter
was completed in a single act ; but here there is required a great
number of successive acts, whose capacity to unite at all in a
common effect is simply due to the fact that they are all of a
similar nature. That is, the process which gave rise to the
space-perception of the sense of sight must be many times
repeated for the sense of touch. Now just as we normally fixate
with the yellow spot anything that we wish to apprehend clearly,
so will the blind be compelled by the great difference in the
sensibility of the various parts of the skin to make exclusive
perceptional use of those portions which are capable of the
finest discrimination. The parts of the organ of touch which
possess this capacity in a pre-eminent degree are the hands. The
blind are constantly practising their hands in touch, and even
more in movement. Touch-sensations alone can obviously
never suffice for the exact apprehension of spatial relations. The
reason for this is that if the parts of an object do not lie
exactly in the same plane, the cutaneous pressure-sense is un-
able to give any account of them. Hence the slight tactual
movements of the hands, and especially of the fingers, which in

Why are not Visual Objects Inverted? 163

the blind are wonderfully active, are of very great importance.
By their means the spatial properties of objects are more
accurately apprehended, partly through successive contact with
the parts of the organ of touch which are capable of finest dis-
crimination, partly owing to the continual connection of sensa-
tions of pressure and of movement. But we always find that
the blind do not apprehend even fairly simple spatial relations
with anything like the rapidity with which the perceptions of
sight enable us to obtain an adequate idea of the most compli-
cated figure. Their sensations of touch and movement have to
construct the object gradually for them out of its parts.

§ V

Thus the slow and imperfect development of the spatial per-
ceptions of the accidentally and congenitally blind confirms our
assumption that the sense of sight normally outruns that of
touch. In holding this view, we are in conflict with the opinion
which was generally current in the older psychology, and is not
yet entirely abandoned, — the opinion that the sense of sight is
more probably educated by the sense of touch. What we grasp
with our hands, it was said, is more certain to our sense-percep-
tion than what affects us at a great distance. It was forgotten
that both objects alike make an impression upon the sensory
nerves, and that these, in the absence of correlated psychical
processes, can have nothing to say regarding the origin of the
impression.

But there was an especial circumstance which seemed to sup-
port the view that the sense of touch was necessary for the
development of that of sight. We see objects in their natural
position, and not inverted. But the images which external
objects produce upon the retina are reversed. The eye is an
optical apparatus composed of a series of curved surfaces, which
cast upon the retina a miniature image of all objects lying within
the field of vision. The spatial relations of this image, however,
are exactly the reverse of those of the object itself: if the latter
stands upon its feet, the retinal image stands upon its head, and
vice versa. So long, therefore, as it was supposed that the act
of vision is concluded with the formation of the retinal image,
our vision of objects the right way up necessarily remained a

164 Lectures on Hitman and Animal Psychology

paradox. But what does the mind know of the retinal image ?
We have only learned of its existence and its inverted position
as regards the object from the physicist and physiologist. In
order to be able to perceive this image as it really is, we should
have to assume another eye behind the retina. And, as a matter
of fact, this hypothesis has now and again been considered a
probable one. It was never said, of course, that there is a real
second eye ; but it was supposed that when the image affected
the mind it was again inverted by it, just as it would be by a
second eye, — apropos of which an ingenious philosopher has
remarked, not unjustly, that, instead of ascribing to the mind
this perpetual business of inversion, it would be much simpler to
stand it on its own head, so that its inversion might set right
again the inverted world imaged on the retina.

From the standpoint of our own investigation of spatial vision
this difficulty is capable of a very simple solution. It is merely
as a series of locally-coloured sensations that the retinal image
affects our mind. Only by the movement-sensations of the eye
does the mind learn to connect these into a spatial order. But
what do the movement-sensations tell us about the position of
objects ? As the eye moves it passes from point to point of an
external object. In moving round its centre from above down-
wards, it passes over an object from top to bottom. It brings
all the parts of its retinal image successively upon the spot of

clearest vision. Now when the visible
portion a of the eyeball moves down-
ward in front, the yellow spot g at the
back will be turned upwards (Fig. 23) ;
as the front points fixates the different
FlG> 23 parts of the object, the point g tra-

verses the retinal image in precisely

the same way. So that, if the position of objects in space is
inferred from movement, the retinal image must be inverted,
since only where this is the case is it possible for the movement
to correspond with the actual position of the objects. So far
from being a paradox, the inverted retinal image is necessary for
vision. The retinal image must have been upside down, even if
the laws of the refraction of light in the eye had not rendered
the inversion physically necessary.

Why are not Visual Objects Inverted? 165

Of course the further question may be raised, how we know
that we are moving the eye up or down. Are not 'up' and
'down ' relative notions, which presuppose the perceiving subject
and his position in space ? It is really just because up and
down are only relative that we are able to introduce order into
the world of spatial vision. If we had perception of absolute
direction up and down, we should be obliged to think that either
by day or by night, as the case might be, we stood upon our
heads ; that would follow necessarily from the rotation of the
earth. The reason that we do not think so is, that we make
ourselves the central point in all space-references. Up and down,
like right and left, are terms which only have a meaning when
referred to ourselves. In distinguishing an upper and a lower
in our spatial perceptions, we make continual reference to our own
body : we call that ' down ' which for our eye lies in the same
direction as our feet ; we call everything 'up' which lies in the
same direction as our head.

There still remains one objection, which seems to tell against
the influence of movement upon spatial sense-perception, which
we have already recognised and indeed proved to exist in
numerous cases. Do we really always move our eyes, it might
be asked, when we wish to see things spatially ? Must we
actually turn the eyeball up or down in order to know what is
above and what is below ? By no means. Without moving our
eyes in the least, we can apprehend objects as spatially ex-
tended, and assign to each its own spatial position. How shall
we attempt to meet this objection ? We might, as has been
sometimes done, point to the great rapidity of the ocular move-
ments, and our consequent inability to observe them. It might
be assumed that though we think our eye is at rest, it is in
reality executing very rapid movements. But we cannot escape
the difficulty in this way : the rapidity of the muscular move-
ments is by no means so great as we should be obliged to
assume that it was on this hypothesis. And, on the other
hand, we are able experimentally to reduce the duration of a
light-impression so greatly as to entirely exclude the possibility
of eye-movement during its operation ; e.g., by illuminating
instantaneously with the electric spark. Under these conditions
objects are still seen spatially. There can be no doubt, there-

1 66 Lectures on Human and Animal Psychology

fore, that movements are not requisite for every single spatial
perception.

But there is another point that must not be lost sight of. We
must always distinguish mental processes from mental products.
The latter may depend upon a capacity acquired in the course
of previous development. It is not necessary that what was at
first a factor in the formation of our space-perceptions, and is still
operative to perfect and refine them, should on that account be
a persistent and inevitable condition of all vision. The child,
taught by its mother to make the first step, learns in time to
run alone. Why should there not also' be conditions of vision
which are operative solely, or at least principally, in the first
stages of the development of this sense ?

As a matter of fact, we have already discovered conditions of
this kind. The relative position of the sensitive points of the
retina is determined by a series of intensively graduated move-
ment-sensations, standing in associative connection with corre-
lative, locally coloured light-sensations. If the impressions
once experienced are given a second time, these points can be
recognised by their local colouring. So that if two impressions
affect two retinal points which were on a previous occasion
separated from one another by a movement-sensation of definite
intensity, we shall be able, after frequent repetition of the whole
process, to distinguish them without the actual occurrence of
the movement and its attendant sensation. When once the
local sensation-differences have obtained from movement-sensa-
tions the measure of the distance which separates them, they
retain this measure in independence of its source. A definite
place- reference is attached to the local colouring, behind which
its true character as qualitative property of sensation entirely
disappears. We imagine that we perceive directly the locality
of an impression, while in reality we are only perceiving a
peculiarity of the sensation, and from it recognising the locality.
And when we have extended our power of spatial discrimination
by practice, we think that our capacity for the apprehension of
spatial differences has been directly increased, whereas in point
of fact it is only our ability to discriminate small sensation-
differences which has improved. What is true for sight in this
regard holds also for touch, only that the latter (even when it

Remarks upon the Theory of Space-construction 167

has attained an unusually high degree of development) stands
in constant need of further assistance from movement-sensations
on account of the less definite character of its local sensation-
attributes. So that the name ' sense of feeling,' which is some-
times used for touch, is significant. Originally we 'fee) for'
objects with the eye as we do with the hand. But the hand
remains simply an organ of ' feeling,' not only because it must
come into actual contact with the objects which it is to perceive
while the retinal image is produced by the action of light at a
distance, but also because it goes on to 'feel over' after contact
has taken place; and a complete perception is only gained by
the combination of the two kinds of sensation, — pressure and
movement.

§ VI

I have attempted to describe the phenomena of spatial sense-
perception, in such a way that the theory which is to explain
and co-ordinate them results of itself. The theory which I
have given you is directly suggested by the facts, and does not
attempt to go beyond them. But at the conclusion of our
considerations, we must not omit to state that there are both
physiologists and psychologists who still believe that they can
dispense entirely with any such explanation of the arrangement
of our visual and tactual sensations, or, at least, think that one
of the factors discussed above suffices to explain all the facts.
In the former case, it is assumed, — as was uniformly done in the
older physiology, — that the spatial arrangement of our ideas is
given directly in the arrangement of the parts of the retinal
image ; or, as it is put to-day with more show of learning,
though without any real improvement in the form of expression,
that every sensation of the two senses with which we are here
dealing possesses from the first a certain spatial quality. Now
we cannot deny that this would be the most convenient
hypothesis possible. But it is equally undeniable that it is
totally unable to take account of all the factors which we have
found to exercise a determining influence upon our apprehen-
sion and estimation of spatial magnitudes. Where the attempt
has been made to do justice to the factors in question from this

1 68 Lectures on Human and Animal Psychology

point of view, it has been found necessary to set up a number
of artificial and complicated secondary hypotheses, some of
which even go the length of self-contradiction. These may,
perhaps, possess a certain value for the logician, as warning
examples of how hypotheses should not be constructed ; but
they are absolutely useless to the psychologist.

The case is different when an attempt is made to furnish a
theoretical explanation of space-construction in terms of one of
the influences which determine the act of perception, to the
neglect of the others. It has often been thought possible to set
up a theory in terms of movement and movement-sensations
alone, and either entirely to neglect the local sensation-qualities
of the retina and skin, or to regard them as functioning in
entire independence of movement, and as being, like the latte^
sufficient in themselves for an adequate explanation of the facts.
The first of these views inevitably leads to the conclusion that
muscle-sensations as such possess a special space-quality ; the
latter ascribes this quality to the retinal sensations alone, or to
both of these sensation series. So that there is indirectly
implied a return to the view that the extensive idea in general
neither demands nor is capable of any psychological explana-
tion. But it is not enough to grant that the spatial arrangement
of impressions is determined on the one hand by movements,
and on the other by properties attaching to the resting sense-
organ and connected with the place of the stimulus. Ex-
perience shows that these two influences are so intimately con-
nected that neither of them is operative without the other. The
principal proof of this is found in the fact that effects which
can only be explained from the laws of ocular movement still
persist when the eye is at rest ; cf. the case of momentary
illumination by the electric spark. The above-mentioned
illusions with regard to the relative lengths of horizontal and
vertical lines and other similar phenomena do not disappear
when movement is prevented, although they may sometimes be
less striking,

If, following Lotze, we call every constituent of sensation
which may be of influence upon the act of spatial ideation a
local sign, the theories which hold that space- perceptions have
been generated by psychological processes, and are neither

Remarks upon the Theory of Space-construction 169

given a priori nor result from a special quality of sensation,
may be distinguished as the theory of simple and the theory of
complex local signs. The first assumes either local signs of
movement-sensations, or local signs of the skin, or both, with-
out, however, in the latter case admitting the interaction of the
two. The theory of complex local signs, on the other hand,
regards the extensive idea as the mental resultant of intensively
graduated local signs of the movement-sensation and qualita-
tively graduated local signs of the sensory surface. Space-
perception depends on the uniform association of these two
sensation series, although the members of one of them need
only be reproduced in order to be effective. This is especially
true of the intensive series, whose terms are so intimately con-
nected with those of the other, qualitative series, that every pair
of definitely different local signs will be invariably associated
with the movement-sensation corresponding to the passage of
the organ over the distance between them.

LECTURE XI

§ I. THE SEPARATION OF VISUAL IDEAS ; INFLUENCE OF BOUNDARY
LINES. § II. IDEAS OF DEPTH. § III. RELATIONS BETWEEN
APPARENT MAGNITUDE AND DISTANCE OF OBJECTS.

WE have now shown at some length how the mind comes
to arrange visual impressions in spatial order upon a
plane surface. But our knowledge of the formation of the field
of vision has given us no idea either of the nature of external
objects, or of the visible parts of our own body. The impres-
sions, though spatially disposed, have not as yet been brought
into those relations in virtue of which they are arranged as
separate ideas, each apprehended as a whole of definite spatial
form. How does this separation come about ? How do we
pass from the spatial perception which leaves its objects side by
side without distinction or difference to the idea of objects
which are spatially separate ?

First of all, it is plainly the boundary lines of objects which
separate them from one another, and further divide up a single
object into parts. They afford a definite resting-place to the
fixating eye. Whenever we have a series of objects suddenly
presented to us, the eye is arrested by the sharpest boundary
lines. It thus learns the rough outlines of objects first, and
from these passes by degrees to the finer delineations of their
parts. This influence of boundary lines on the movement and
fixation of the eye may be easily proved by experiment. We
hang, e.g., before a white surface a number of vertical black
threads of different diameter, and allow an observer to look
through a tube towards the screen in such a way that the threads
lie in his field of vision. Supposing that the observer knows
nothing beforehand of the arrangement and nature of the

The Separation of Visual Ideas 171

threads, he will be sure to say when questioned that he saw
the thickest thread first, and the others afterwards, for the
most part in the order in which their distinctness brings them
to consciousness. And a little attention will lead him to dis-
cover that in the first moment of looking through the tube the
eye turned by a kind of mechanical necessity to the sharpest
outline in the visual field, and then, after clearly apprehending
this, directed itself successively upon the others in the order of
their attraction. This order remains constant if the threads are
hung at different distances, except, of course, that the influence
of distance upon the apparent thickness of the threads must be
taken into account. If two threads of the same diameter are
hung at convenient distances for vision, the nearer one is
apprehended first. But if their diameters are unequal, that wilt
be first seen which makes the stronger impression upon the eye ;
so that the boundary lines appearing in our field of vision
determine on the one hand the movements of the eye, — the
image of the boundary line being brought upon the place of
clearest vision, — and on the other that process within the eye
whereby it adapts itself to the distance of the objects viewed.
This internal process of adaptation for near objects is also a
muscular movement attended by sensation. And the sensation
furnishes a measure of the amount of adaptation : the nearer
the object we are looking at, the greater the convexity of the
crystalline lens under the action of the intra-ocular muscles.

This tendency of the eye to fixate distinct points, or boundary
lines, can only be explained by reference to a mechanism similar
to that concerned in reflex action. Indeed, it seems to be a
justifiable assumption that the relation of movements of the
eyeball and of the muscles of accommodation to boundary lines
and points is nothing but a further development of reflexes
present in the eye from the very first. During the first days of
a child's life, every light-impression produces an' ocular move-
ment, which brings its image to the place of clearest vision.
But as the retina is continually affected by uniformly diffused
light, that which is distinct and definitely bounded will very
soon be separated out from this indefinite chaos of light-
impressions, forming as it does a special stimulus, quite
different from its uniform surroundings. To such a stimulus

172 Lectures on Human and Animal Psychology

the eye turns ; and when several are present, to each in succes-
sion, — the order of fixation being determined in every case by
intensity, i.e., by the degree in which each stimulus differs from
its surroundings. Even when the sense is completely developed,
visual apprehension occurs with the mechanical necessity
peculiar to reflex movements. And though we may voluntarily
counteract this constraining influence, yet we are always falling
again under its sway whenever the unexpectedness of an
impression or some other particular reason renders an act of
will impossible.

The influence of boundary lines and of points is modified by
a third factor, which is dependent upon the same conditions
and is operative in the same way as these, namely, the movements
of objects, by which their position relatively to one another and
to the perceiving subject is changed. Since every object which
is marked off from its surroundings by boundary lines forms a
permanent whole, however its surroundings vary, it becomes
the object of a particular idea. If objects at rest are appre-
hended as similar units, that is only because this characteristic
of limitation points to a separation from their surroundings such
as is matter of immediate observation in every case of move-
ment. In the series of separate ideas obtained from the original
fields of vision in this way, through the medium of movement
and boundary line, the first place is taken by the body of the
perceiving subject, whose permanence gives it a preference over
all other objects, — while, besides that, as the substrate of ah
sensations and perceptions, it affords the universal centre af
relation for the spatial arrangement of the entire external world.

The sense of sight, then, comes to apprehend objects separately
in space by means of changes in their position and correspond-
ing changes in boundary line. Another and a final motive to
this spatial separation of objects consists in their reference to
points in space at different distances from the eye. We can
show, even in fully developed vision, how the idea of spatial
depth originates, since the idea is of comparatively late growth.
This is proved conclusively by the experience of the con-

Ideas of Depth 173

genitally blind who have been restored to sight by a surgical
operation. In such cases we find a certain power of orienta-
tion acquired during blindness by the aid, as we may suppose,
of the light-shimmer which is never entirely absent ; but there
is no cognition of distance. Remote objects are not infrequently
regarded as lying close at hand : the patient shrinks back from
contact with them. We may observe the same phenomenon in
the first months of childhood : the baby will reach for the moon
or for the objects seen in the street through a third-story
window.

The development of the ideas of depth is primarily conditioned
by ocular -movements. We let our eye range from nearer objects
to more remote, and the path over which it travels gives us a
measure of the distance of the objects which we have successively
fixated. For a movement-sensation is associated with every
movement,, and its intensity increases with the extent of the
movement. When the relative distances of objects are to be
measured, they must not, of course, cover one another. And,
moreover, their bases must be visible. If this is not the case,
we may quite well estimate objects at different distances from
us as situated close beside each other. You may convince
yourselves of this by holding before the lower half of the eye
a small piece of paper, and so covering the lower part of the
objects looked at. If the difference of their distances is small,
they are generally regarded as at the same distance ; if it is
large, you note, indeed, that one object is nearer, and the other
more remote, but you have no approximate idea of the distance
between them. That you notice any difference at all in these
instances is due to the accommodation of your eye for near and
far. Since adaptation also depends upon a muscular move-
ment, we have a rough measure of the focussing of the eye in
the accompanying muscle-sensation. At the same time we
are obviously less accustomed to attend to this mechanism.
Usually we do not employ it in measurement, but make use of
the movements of the eyeball, which are much more accurate,
and have a far wider range.

When we pass with the eye from the base of one object to
that of another we usually begin with the nearer. If we are
estimating the total distance of any object from ourselves, we

1 74 Lectures on Human and Animal Psychology

begin from our own feet. So that the foot is the most original
and natural unit for measuring distances : the length of the
foot is the first spatial distance which occurs to us. Now when
we are passing from nearer to more remote objects our eye
moves from below upwards. Suppose we are standing at a
(Fig. 24), and one eye, o, is directed successively upon the more
and more remote points, b, c, etc. Dur-
ing this process it turns upwards ; the
visual axis passes gradually from a po-
sition where it is directed vertically
downwards towards the horizontal, un-
til, finally, when the object is very
remote, it completely attains this latter
FIG. 24. position. This movement is not confined

to the eye : the' head moves as well, es-
pecially for objects lying directly below us, and so assists the
ocular movement. For these head-movements, again, we have
.a measure in sensations of movement ; so that the result is the
same, however the movements which carry the fixating eye
from point to point are brought about.

Since in these movements both head and eye turn from below
upwards, remote objects seem to lie higher than near ones, and
the horizon which bounds our view is at the same height as the
-eye. If the earth were a perfectly plane surface, we should all
imagine ourselves to be standing in a depression ; and the
surrounding landscape would appear to rise uniformly to the
horizon. This phenomenon is, of course, modified in various ways
by all sorts of inequalities in the earth's surface, and also in part
"by the spherical form of the earth. Since, again, distances
which are objectively equal require a lesser eye-movement in
passing over them the farther they are from us, more remote
objects seem to lie closer together than those which are nearer.
So that we are frequently unable to cognise a difference of
distance in the former case which is quite obvious to us in the
latter. If you look at the angles I, 2, which are subtended by
the equal distances a b, b c (Fig. 24), you will see that these
angles, which give a direct measurement of the magnitude of
-the ocular movement, become smaller and smaller, and will at
last entirely disappear. But if we take a more elevated position,

Ideas of Depth 175

so that our eye h at </, our field of vision is at once extended,
and remote distances become visible which were previously
hidden from our view. Near distances appear, on the other
hand, relatively smaller than they were before. So that if we
climb a mountain, or ascend in a balloon, all objects, near and
remote alike, appear closer to us.

Objects situated at different distances from the observer pre-
sent differences not only in the relative position of their bases,
but in a whole number of other properties. Originally these
are turned to account only when associated with judgments of
distance in terms of eye-movement, but later they may become
independent indications of distance. To this class belong pri-
marily the shadows cast by objects. Their direction and magni-
tude are dependent on the position of the source of light with
regard to the object, and of the object in relation to the point
of view of the observer. Then, again, increase of distance means
gradual decrease in clearness of boundary lines. And the more
remote an object, the paler will be its colouring, which will
also vary in quality according to the absorption of light by the
atmosphere. All these factors together make up those con-
stituents of perspective in drawing and painting which enable
the artist, by proper distribution of contours, light and shade,
and colour-tones, to produce upon a plane surface the illusion
of actual tridimensional relations.

When the distances are very great, the apparent magnitude of
the objects comes into play as a further factor. It furnishes the
most obvious standard of measurement when we are comparing
quite distant objects, and in cases where the above-mentioned
factors of perspective are absent is our sole criterion for the
estimation of distance in the third dimension. If we compare
a tree which is ten feet off with another whose distance is a
hundred feet, the former appears larger, even though we know
that the two are objectively equal. The magnitude of an object
which is directly given in perception we term its apparent mag-
nitude. Whenever we have learned from repeated experiences
the actual magnitude of an object, its apparent size is employed
as a measure of its distance from us. This is not the result of
an act of reflection on our part, — that is never involved in the
process of perception, — but is due to the direct association of an

176 Lect2ires on Human and Animal Psychology

idea of distance with the impression. The development of this
idea, however, is dependent upon experience ; and we must
therefore explain it itself as the result of an association between
the distance of an object whose real size is known and the
apparent magnitude of that object. The apparent magnitude
of a person approaching from a distance will therefore excite
directly the idea of his distance, because in many previous in-
stances we have associated the idea of this particular distance
with this particular magnitude by means of other characteristics
directly given, and especially by moving the eyes from our own
feet to his.

§ HI

The apparent magnitude of an object and the magnitude of
its retinal image are usually regarded as directly proportional.
The obvious reasons in support of this view are that both de-
crease with distance, and that plainly the magnitude of the
retinal image must be the principal condition of our having any
idea at all of an object's apparent magnitude. If some one is
approaching us from a distance, his image upon our retina and
his apparent size (i.e., the size which \ve ascribe to him in idea)
increase at the same time. But since this idea of apparent
magnitude is the product of numerous associations, some of
which are quite complex in character, we ought not to expect
to find any constant relation between the two values, — that
of the retinal image (physiological) and that of the idea (psy-
chological). This presumption is confirmed by experience. For
we find that while the magnitude of the retinal image remains
constant, or, what is the same thing, that of the visual angle
formed by drawing lines of vision to the boundaries of the
object, the apparent magnitude may be extraordinarily different,
owing to its determination by the other factors which enter
into the association. Foremost among these stands the idea
of distance suggested by other characteristics of the object ; and,
in the second place, there comes into account the idea of the
magnitude of similar objects.

The most striking instance of our seeing the same object at
the same distance sometimes as larger, sometimes smaller, is

Apparent magnitude and Distance 177

the one afforded by the sun and moon. At the distance which
separates the sun from the earth the size of its image cannot
differ at morning, noon, or evening ; its magnitude remains equal
at all times of the day. But when the sun is at the zenith it
appears smaller than when it is on the horizon at rising or set-
ting. This is explained in the following way. We form a definite
idea of the distance of the sun, though, of course, the idea is
very far from the truth. The sky seems to our eye a solid arch,
which rests upon the earth at the horizon, and closes down upon
the nearest mountains or the towers of the nearest town. To
frame an idea of the distance of the sun at the zenith, we have
at most only a tower or a mountain as our standard ; to get
an idea of the distance of the horizon, we make use of every
object within our field of vision. Between ourselves and the line
of the horizon we see large numbers of trees, fields, villages, and
towns : and a distance which contains so many objects must
of course be very large. So we come to imagine that the
horizon is farther off than the zenith ; the arch of the sky which
rests upon the earth is not semicircular, but is rather shaped
like a very convex watch-glass. But if our retinal image is
equally large whether that which we are looking at is near by
or far off, the magnitude of the object regarded must be dif-
ferent in the two cases. The remoter object looks to be actually
larger, just because it seems to be of the same size as the nearer
one. It. is as though a man on a steeple should appear as
large as one by our side ; we could not but imagine that the
former was a giant. Before we form an idea of the magnitude
of an object we always consider the distance at which we view
it. Quite frequently we mistake the distance. But though we
may have convinced ourselves of this error a hundred times, we
cannot free our perception from it, so stable are the associations
through which it has arisen. Our perception of the size of the
sun rests upon two wrong ideas : in the first place, we suppose
that it is not much farther off from the eye than the nearest
mountain peak or the top of the neighbouring church spire ;
and secondly, we imagine that it is sometimes nearer, sometimes
more remote, according as it stands at the zenith or approaches
the horizon. We need not be astronomers or physicists to know
that both these notions are false. But however well we may.

N

i/8 Lectures on Human and Annual Psychology

know this, and however sure we may be that our distance from
the sun does not become alternately greater and less, we still
make the same mistake, — the astronomers and physicists among
us no less than the ordinary man.

Our perception of objects is, therefore, always dependent
upon their distance ; not, however, upon their actual distance,
but upon the distance as we imagine it. If we could obtain a
perception of the actual distance of the sun and the moon, they
would appear infinitely large to us. On the other hand, when
we try our best to imagine them quite close, they appear smaller
than usual. If we look at the moon through a tube, or through
the closed hand, seeing nothing but that portion of the sky
where the moon is situated, it will seem no larger than a half-
crown, whereas it generally looks about as large as a plate.
The simple explanation of this fact is that we do not now
localise the moon somewhere behind the trees which fill the
foreground of our normal field of vision, but close behind the
tube or closed hand. In the same way, when we look at the
moon through an ordinary telescope, it seems, smaller, and not
larger, than usual, though the telescope magnifies, and we can
see by its aid a number of things upon the surface of the moon
which are invisible to the naked eye. That is also because the
moon is not localised at a distance, but at the end of the tele-
scope. The same thing happens when we direct our telescope
upon distant mountain peaks : we see their outlines more clearly ;
we observe details which the unaided eye could not distinguish ;
and yet we note that on the whole the mountains do not appear
larger, but smaller. In these cases the magnitude of the retinal
image of the moon or of the mountain is increased, yet we see
the objects themselves as smaller.

But we have not even yet completed our account of the
influences which are here at work. If we look at a man on the
top of a tower, he does not appear nearly so small as he should
do in accordance with our idea of his distance. When we look
at the mirror on the opposite wall, we estimate its distance
pretty accurately. But we see it larger than we really ought to,
if we compare the size of its retinal image with those of other
and nearer objects. Clearly, the fact that we already know the
size of the man and the mirror is here of importance. We have

Apparent Magnitude and Distance 179

seen men close at hand thousands of times, so that we know
certainly that there never was a man only a millimetre high, nor
a drawing-room mirror only two centimetres square. This ex-
perience exerts an influence upon our perception, and serves to
modify the idea which \ve should otherwise have formed regard-
ing the distance of the objects we are looking at. This cor-
rection is, as you know, not complete : the man on the roof is
much smaller to view than the man by our side, and the mirror
on the wall twenty feet away a little smaller than it is when we
stand directly before it. There is a kind of conflict between the
fact that the object viewed is at a distance, and must, therefore,
appear smaller, and the fact that we are acquainted with its
true magnitude. Both sides are, as a matter of fact, right in
this controversy ; but since it is not possible to grant the claims
of both at the same time, we follow the example of that most
excellent judge who decided all lawsuits involving money by
dividing the sum between the two parties in the suit.

Our perception, then, can only determine the true magnitude
of objects where this true magnitude is actually known to us ;
and this knowledge must come from direct and often repeated
experience. However sure we may be that the moon is im-
measurably larger than a plate, we shall not on that account see
it a whit larger. We are convinced that a magnifying-glass
does not make the objects seen through it any larger ; and yet
they continue to be larger for our vision. The sun at midday,
we are certain, is not smaller than it is in the morning, yet as
we look at it it appears smaller. Vision requires to be con-
vinced in a quite different way. No assertion on the part of
other people, no speculation or calculation, is of influence in
determining our perception, but only an association of ideas
repeated over and over again. Isolated experiences, therefore,
make no impression upon our minds. From a window in my
room I look directly upon a neighbouring church tower. The
face of the church clock appears about as large as that of a
moderately large clock which hangs upon my wall. The ball of
the steeple looks about as large as the button of a flag-staff. A
little while ago the clock face and steeple knob were taken
down for repairs, and lay upon the street. To my astonish-
ment, I saw that the former was as large as a church door, and

180 Lectures on Hitman and Animal Psychology

the latter as large as a waggon-wheel. Now the two are in
their places again and look to me just as they did before, al-
though I have learned their true size. The workman upon the
roof does not seem so much smaller than he actually is, because
I have observed the size of my fellow-men hundreds of times.
But the ball of a steeple and a church clock are not objects of
every-day experience. The button of a flag-staff and the clock
on the wall are much more familiar. And so I think of the
steeple knob as the flag-staff button, and the church clock as a
wall clock. Even that idea seems exaggerated, if I compare
these things with objects more immediately around me. For I
can just cover the ball of the steeple with the head of a pin, and
the tower clock with my watch, if I hold these at a little dis-
tance from my eyes. If it were not altogether too improbable
that the steeple should carry a watch and have a pin's head as
its ball, I should perhaps imagine that that was the actual state
of affairs.

We see, then, that our perception of things in space is extra-
ordinarily variable ; that it is conditioned by a number of
influences which by no means emanate from the objects them-
selves ; that we take into account the apparent magnitude of
objects, their distance from us, and finally our experiences of
the same or similar objects in other connections. How, then,
can we assert that our perception is determined by the objects
outside us ? All these influences are not found in the objects,
but in ourselves. It is we who involuntarily and unwittingly
alter the phenomena, in terms of the ideational elements which
are already present in consciousness, ready at a moment's
notice to form associations. And this whole variability of our
world of perception depends primarily on the idea of depth,
which gives to the spatial arrangement of the visual field its
property of being apprehended as at different distances from
the observer. Such a property must necessarily open a wide
field for the play of the most diverse subjective and objective
influences upon our spatial ideas.

But although the arrangement of objects in terms of spatial
distance, under the operation of these influences, must always
remain imperfect and incapable of exact measurement, we must
not forget that through it alone do we obtain a final form for

Apparent Magnitude and Distance 181

our world of ideas. With the reference of objects to different
distances in space, the world of perception is placed outside of
us, and is differentiated into an infinite diversity of content.
Although the spatial relations which we ascribe to external
objects may at the outset often be incomplete and deceptive,
still the decisive step has been taken with the very introduction
of those relations. The ceaseless activity of our sense-percep-
tion is constantly at work in the endeavour to perfect our ideas.
It furnishes us with new ideational groups, and corrects the
most serious errors in those already acquired. All the senses
co-operate in this work, each revising and supplementing the
others. But it is primarily the common action of the two co-
ordinate organs of vision to which we owe the greatest part of
our ideational development. There are no other organs which
so directly supplement and correct each other's perceptions, and
which thus give so great an impulse to the fusion of separate
perceptions into a single idea, as the two eyes.

LECTURE XII

§ 1. BINOCULAR VISION ; DIFFERENCE OF THE Two RETINAL IMAGES.
§ II. THE STEREOSCOPE; SIMPLEST STEREOSCOPIC EXPERIMENTS.
§ III. THEORY OF STEREOSCOPIC VISION.

§1

I ^HE two eyes may De compared to two sentinels who,

viewing the world from different standpoints, impart their

experience to each other, and so complete in idea a common

picture, uniting in itself all that each observer has seen

separately.

It is not very long since the fact was discovered that bino
cular vision was different from monocular. The early physio-
logists thought that the image of an object produced in one eye
was not different from that apprehended with both. And it
was accordingly supposed that the two eyes were simply equi-
valent to a single eye, — a conclusion which found an apparent
confirmation in the anatomical structure of the optic nerves.
At a certain point in their course after leaving the brain, de-
cussation occurs. At this point the nerve-fibres are closely
interlaced ; and then again two nerve-trunks appear, one ex-
tending to either eye. It was supposed that at the point of
decussation and interlacing of the two nerves the fibres were
divided. Each fibre, from whichever side of the brain it came,
was thought to divide in such a way that one of its parts ran
to each eye, and within each eye to correspondingly situated
retinal points. It was in 1840 that the English physicist
Wheatstone proved that the images cast upon the retina of
each eye are very frequently dissimilar, without there being
occasioned any disturbance of vision. If we hold an object
close before us, and shut first one eye and then the other, we

Binocular Vision

see it a little differently in the two cases. Suppose, eg., we
hold our hand between the eyes, at a little distance from them,
so that the surface of the hand is at right angles to the face ; one
eye sees only the back, and the other the palm, of the hand.
If the point of anatomical decussation were really a place of
division, and if the images cast on the two eyes were directly
intermixed in the brain, simultaneous binocular vision would
only give us a confused picture. For on a portion of one retina
there is represented part of the back of the hand, on the corre-
sponding region of the other part of the palm. These two
images would therefore be superimposed in the common act of
vision, and that would render any clear apprehension impossible.
But observation by no means confirms this view of the matter.
It is rather the fact that we see the hand more perfectly with
two eyes than with only one. It is not merely that we see
simultaneously much that in monocular vision could only be
apprehended successively ; but we perceive directly that the
hand is not a picture painted on a surface, but has extension in
the third dimension. The same test may be repeated with the
most diverse objects ; we shall always find that the apprehen-
sion of the third dimension of objects is intimately connected
with simultaneous binocular vision. If we are using simply
one eye, we are often unable to decide whether the fixated
object is tridimensional, or merely a drawing upon a plane sur-
face. So that in monocular vision illusions are possible in this
connection ; drawings in perspective and light and shade in
particular may give a very strong impression of the third
dimension. If the object is near to us, the illusion vanishes at
once so soon as the second eye is opened. Although, there-
fore, a perception of the third dimension may be gained with
a single eye, it is always less complete, instantaneous, and
immediate than that given in binocular vision. As a rule we are
only able in monocular vision to attain to a perception of the
third dimension of objects by degrees, and in terms of the move-
ments made by the eye in passing from a nearer point to one
more remote, i.e., by a series of acts following one another in
time.

If, then, the immediate idea of depth is always connected
with simultaneous binocular vision, it seems obvious to say that

184 Lectures on Human and Animal Psychology

we see objects in this way more adequately just because the
images cast upon the two eyes are different. We have a direct
perception of extension in the third dimension because the two
eyes look at things from different points of view. And this
fact is, moreover, confirmed by observation. When we remove
the object farther and farther from the eye, the perception of
depth disappears. But with increase of distance the difference
between the retinal images grows less. And at last, when the
object is so far off that the distance between the two eyes is
practically zero in comparison with it, the two images are pre-
cisely alike, and fall upon correspondingly situated portions of
the two retinae. If, e.g., we hold a sheet of paper close before
the eyes, so that the right eye sees one side and the left the
other, we get a clear idea of its extension in the third dimension.
But if it is removed farther and farther off, we come to see less
and less of the two sides ; and at last perceive nothing but the
front edge, which is just the same for one eye as it is for the
other. In other words, perception of depth and difference
between retinal images always run parallel to each other.

If this difference between the retinal images of the two eyes
is the cause of the perception of depth, it is obvious that this
perception may be induced without any actual vision of a
tridimensional object, simply by presenting to the eyes retinal
images having differences similar to those produced by the per-
ception of such an object. If, that is, we cast upon one retina
an image which looks like the back of the hand seen obliquely,
and upon the other an image which resembles the palm of the
hand seen under similar conditions, an idea of extension in the
third dimension will arise in our minds, although the images
employed are simply drawings upon a plane surface. The
retinal images are precisely the same as they would have been
had we looked at an actual hand ; the result as well must there-
fore remain unchanged.

It is quite easy to test this. And it is best to take for the
purpose objects of fairly simple form. Suppose that we are
holding before our eyes a truncated cone with circular base, the
apex turned towards the face. First, we close the right eye,
and draw an exact picture of the cone ; now we close the left,
and make a similar drawing. The two pictures are different,

Binocular Vision 185

because the right eye sees parts of the object which the left
does not, and vice versa. The left eye sees the cone approxi-
mately as A, the right as B (Fig. 25). Neither of these views
as mere drawing furnishes any incentive to an idea of the third
dimension. The most that we can do is by an effort of imagi-
nation to see the small inside circle at will either nearer or more
remote than the larger outside one. But if we let A affect the
left eye as though it were an image proceeding from an actual
cone, and B act similarly on the right eye, we have just as
definite an idea of tridimensionality as we gain by observing
the cone itself.

It will not, of course, do to view the two drawings with both
eyes directed quite at random. We must look at them in a
way which corresponds to the formation of images by actual

FIG. 25.

objects. The left eye must fixate the smaller circle in A, the
right the smaller circle in B. Only under these conditions are
the two images in the eyes related as they would be if we
fixated the top of a real truncated cone. But the experiment is
not altogether easy. We are accustomed to direct both eyes
upon one and the same point. Here we have to fixate a
different point with each, the top of A with the left, the top of
B with the right. Only long and continued practice can enable
us to command our eye-movements to the extent required for
independent fixation by either eye. Normally the movements
of the two eyes are completely concurrent. The movements
themselves are determined by external impressions ; and it is
probable that these were also originally instrumental in bring-
ing about the functional concurrence. For, as we have seen, it
is a law of the reflex mechanism of each eye that our gaze is

i86 Lectures on Human and Animal Psychology

always attracted by distinct points or boundary lines, and
moves from one to the other of these according to the intensity
of the impression to which they give rise. Since both eyes
follow the same law, their movements must necessarily be
closely interconnected ; the point which leads one eye to fixate
it will also arrest the other. Thus there arises an impulse to-
common fixation on the part of the two eyes, which can only
be overcome by practice.

§ II

To obviate this difficulty, which confined observation to a
few practised individuals, Wheatstone constructed the stereoscope.
By means of this instrument any one may readily obtain an
idea of the third dimension from representations upon a plane
surface. The ordinary form of the stereoscope is that given it
by Brewster. It contains two small angled prisms, behind
which at a little distance are placed the drawings to be com-
bined. In free vision the eyes must have their axes parallel in
order to fixate the drawings b simultaneously. But if the
o o prisms/ are introduced, and their refract-

ing angles turned towards each other, the
rays coming from the drawings b will be
diverted in such a way that these fall
upon the place of clearest vision and
adjacent parts of the retinae, although
the two eyes do not fixate the drawings
b, but the point F. The necessary result
then is that the inner circles of A and B
(Fig. 25) affect coincident points of the
two retinse, and the remaining portions of
the figure exhibit precisely the same differences in the retinal
image as arise when we directly observe a real object of similar
character.

The following are the simplest stereoscopic experiments.
The perception of depth will arise if two vertical lines at
different distances from one another are presented to each eye
in the stereoscope ; e.g., the lines a b to the left eye, the lines

\ /

\ /

\t

=J p

6 1< b
FIG. 26.

The Stereoscope 187

c d to the right. We obtain in this way a common image of
two lines, the first of which, I, is due to the fusion of a and
c, the second, 2, to the fusion of b

and d. The former lies in the plane lv b e d ' -

of the paper, the second at some
little distance behind it. This is in
accordance with what would nor-
mally be the case. When we fixate
binocularly two lines the right one F '

of which is farther off than the left,
the horizontal distance between the two lines in the retinal image
of the right eye is necessarily greater than in that of the left.

The idea of depth arises in the same way when we present
to either eye a line drawn somewhat obliquely, and make the
inclinations of the two lines a little different If the lines / and
r, which fall upon the left and right eye respectively, have the
inclinations indicated in Fig. 28,
we obtain a common image, s,
which extends into the third
dimension, its upper extremity
being more remote than its
lower. If, on the other hand,
the lines are inclined as in FIG. 28.

Fig. 29, we obtain a common
image whose lower extremity is more remote than the upper.

These two cases in which oblique lines are differently inclined,
or the horizontal distance between vertical lines is different, are
realised again and again under the conditions of tridimensional
vision with the naked eye, and also in the stereoscope. They
constitute the two fundamental ex-
periments of stereoscopic vision. The
vertical or oblique lines need not be
straight ; the result is the same if they
are somewhat curved. All stereoscopic
vision depends ultimately upon the
combination of these two fundamental FIG. 29.

experiments. On the other hand, we

can never obtain the idea of depth if horizontal lines of
different distances are presented. This is very easily explained

1 88 Lectures on Hziman and Animal Psychology

when we remember that no such condition of tridimensional
vision exists in nature. We may turn and twist an object as
we will ; its boundary lines are always either vertical or oblique.
The facts of stereoscopic vision prove indisputably that the
two eyes perceive independently of each other, and that their
perceptions are only secondarily combined in a common idea.
Any other view as to the causes of stereoscopic phenomena
becomes involved in inevitable contradictions. It is, e.g., abso-
lutely impossible to maintain that the two eyes are really only
one ; that every nerve-fibre divides into two branches, which run
to exactly corresponding points of the two retinse. If this were
so, the common image which we obtained from our truncated

cone would be of the character indi-
cated in Fig. 30, where those parts of
the drawing which do not fall upon
corresponding retinal points simply
cover one another ; but there is no
hint of the origin of an idea of a
simple tridimensional object.
FIG. 30. If we admit, as the phenomena in-

evitably compel us to do, that the two

eyes are separate organs of vision, which sense independently of
•jach other, we can only look for the fusion of the two visual
perceptions in some psychological process. As a matter of fact,
the phenomena themselves lead to this conclusion. We see
that the idea of depth only arises when the two images exactly
correspond to the views which we have of an actual body in
space ; and we find that the direct perception of the third
dimension always implies binocular vision. Suppose now that
the two plane pictures were laid separately before you, and you
were told that they were two projections of one and the same
object, what inference would you draw as to the nature of this
object? You would say, of course, the object is extended in
three dimensions ; and would even possess a tolerably correct
idea as to the extent of its third dimension, and perhaps be able
to construct an exact model of the whole object. If the per-
ceptions of the two eyes are originally two separate things, it
must be by an essentially similar method of procedure that we
come to fuse these separate areal images in the common idea of

The Stereoscope 189

an object extended in the third dimension. We, too, must con-
struct our idea of the model of the object from its areal projec-
tions. The only difference is that we do not do this consciously,
but unconsciously and involuntarily, by an act of sensational
association : so that it is only the result, the idea of the object
itself, which appears in consciousness.

The necessity of fusing perceptions in the idea of a single
object rests in part in the infinite number of these perceptions.
Again and again there are presented to our two eyes corre-
sponding and supplementary areal projections of tridimensional
objects. Always and invariably must we perceive such objects
from the different points of view of the external world obtained
through our two eyes. But this constant motive to connect the
two partial ideas is only half the matter. Another and stronger
influence is found in the mental endeavour which dominates all
perceptive processes, — the effort to obtain a permanent associa-
tion of simultaneous ideas and ideational elements. We have
found this endeavour operative in the processes of areal and
tridimensional perception of which we have already spoken.
There can be no doubt that the fusion of the two visual images
is the result of an act of mental association. But we have
still to determine more precisely how this association takes
place.

When dealing with the formation of the perceptions of the
single eye, we found that sensations of movement furnished a
measure of the spatial distance of separate points in the visual
field. Similarly in the binocular idea of depth it is sensations
of movement which furnish our primary measure of spatial dis-
tance. If the common field of vision contains a single bright
point, the reflex mechanism which governs the relation of
ocular movements to the yellow spot brings about the fixation
of this point by both eyes. Its image falls on the yellow spot,
the place of clearest vision ; i.e., it is the point of intersection of
the visual axes. If other bright points appear in the common
field, they are successively apprehended in the order in which
their intensity stimulates the tendency of the eye to move. So
there results a successive fixation of the distinct points or
boundary lines present in the field of vision. But there will
necessarily arise at once important differences between the

Lectures on Human and Animal Psychology

various cases in which the eyes mark out an object in this way
point after point. If the points which the eye passes over lie on
a plane surface, the image of the points which are no longer
fixated, — whose image, that is, falls not on the yellow spot, but
on the lateral portions of the retina, — still affects retinal points
of approximately coincident position in the two eyes. With
this coincidence of position there is also given a certain simi-
larity of the peculiar sensational colouring, dependent upon the
place of the impression. If, on the other hand, the points suc-
cessively fixated lie at different distances from the eye, the
image of the point which is no longer fixated does not fall upon
points of coincident position and analogous sensational charac-
ter in the two retinae. And this divergence will be greater the
greater the distance in the third dimension which separates the
points. There will necessarily be an essential difference in the
Association of the two visual images in this case ; and the two
series of actual experiences, corresponding to the perceptions of
surface and of depth, will be clearly distinguished from one
another.

§ HI

We must, however, ask how this distinction can give rise to
the peculiar idea of a tridimensional object as opposed to an
areal object. On this point different opinions may still be en-
tertained. It is certain, say many authorities, that only images
which fall upon coincident retinal points are seen as simple ; all
others are seen as double. We possess, therefore, a sure criterion
of the presence or absence of the third spatial dimension in the
presence or absence of double images. And the distance which
separates these, — i.e., the magnitude of their deviation from a
coincident retinal position, — allows us to infer directly the
magnitude of extension in the third dimension. So that the
perception of depth consists simply in the neglect of double
images ; and the idea of depth arises more clearly, the more
there is to neglect in order to attain to the perception of a
single object.

This view cannot, however, stand the test of experiment If

Theory of Stereoscopic Vision 19 J

Fig. 31 is introduced into the stereoscope, the left eye receives
the image A, the right eye that of B. The lines i and 2 fall
upon corresponding parts of the retina,
lines i and 3 upon differently situ-
ated portions. The result is that the
two heavily drawn lines I and 3 are fused
to a single idea, the line arising from
their fusion giving a clear perception of
depth, while the fainter line 2 crosses it
in the plane of the paper ; that is, our
vision has combined into one the two

lines which fall upon differently situated portions of the retinae,
while the two lines which fall upon corresponding parts are
perceived separately. It follows necessarily from this that the
idea of depth cannot arise from the apprehension and subse-
quent neglect of double images. Were that the case, it would
not be possible for the images of I and 2, which are cast upon a
series of corresponding points, to appear separately as double
images. This experiment also proves therefore that the forma-
tion of a visual perception is an ideational act based upon an
association of two visual perceptions, and determined not only
by the position of the retinal images, but also by other proper-
ties which these images possess. The two strongly drawn lines
force themselves first of all upon perception, and they alone can
be referred to a single object when the images of the two eyes
are compared ; while the object itself must extend in the third
dimension of space to the position occupied by the images.

The idea of depth is, therefore, not produced by disregarding
or by intensively weakening the separate perceptions in the
common act of vision, but rather by the clear apprehension of
them and their subsequent combination, — this primary associa-
tion being further associated with other similar ideas. The
differences of the two retinal images are by no means to be
disregarded as worthless inaccuracies. They give us, on the
contrary, an extraordinarily exact measure of the spatial
qualities of external objects. And the inference is unavoidable
that if we perceive these spatial properties through the differenc
of retinal images, these must themselves be given in perception
•with their characteristic spatial differences.

192 Lectures on Human and Animal Psychology

But some doubt may still remain regarding the manner ih
which these differences of the retinal images, whose comparison
gives us the idea of depth, are themselves apprehended and
elaborated into that idea. We must set out from the fact that
the movement-sensations of the eyeball which inform us of the
spatial relations of the areal field of vision furnished also, — at
least, originally, — a measure of distance in the third dimension.
The hypothesis then appears probable that the idea of depth has
been generated by movement. We have already discussed the
signification of eye-movement for the estimation of distance.
If we are fixating an object binocularly, any increase or
decrease of its distance from us is very distinctly perceived by
means of the movements of convergence or divergence, which
are made by both eyes in keeping the object constantly fixated.
We become conscious of these movements by movement-sensa-
tions, and by these latter we measure the approach or removal
of the objects. If a spatially extended object lies before us, it
simply presents to us simultaneously what is perceived succes-
sively when an object moves. At the same time, though the
tridimensional object lies before us as a whole, we can only
clearly apprehend some portion of it at any single moment. In
this case also, then, we pass gradually by ocular movements of
convergence and divergence from nearer to more remote points,
or from more remote to nearer. In this way we perceive what
is nearer or more remote in the object, just as we observe the
changes in the position of a single point when it is in motion.

It can hardly be doubted that the idea of depth originally
arose in this way by a succession of sensations and perceptions.
But it is a different question whether it continues to arise in thr
same manner, whether each single idea which has been gradually
acquired by both eyes continues to be formed by a series of suc-
cessive acts. We have already discussed a similar question in
our investigation of the perception of plane surfaces. There, too,
movements play an important part. But we saw that move-
ments are by no means continually operative in every single
perception, but that the resting eye is itself able to see things in
space, and possesses a fairly accurate measure of spatial exten-
sion. And we found that it was the presence of a local colour-
ing in visual sensations which enabled the eye to dispense with

Theory of Stereoscopic Vision 193

the unremitting action of these movements. These local signs
are permanent attributes, which, when once their relation to
sensations of movement has been discovered, suffice to bring
sensations into the extensive form.

And the idea of depth, which in binocular vision comes in to
complete our simple apprehension of visual space, may also arise
when the eye is wholly unmoved. It often seems to appear
at the very moment when the eye is affected by an' impression
of light, so that there would be far too little time for its forma
tion from a number of successive perceptions separated by
movements. This can be shown very beautifully and con-
clusively if an observer is allowed to look into a stereoscope
in the dark, and the stereoscopic pictures are then suddenly
illuminated by an electric spark. The duration of the electric
spark is so small that there is no possibility of eye-movements
during the time of its occurrence. Nevertheless, if the pictures
are sufficiently simple, there arises immediately after their illu-
mination by the spark a clear idea of extension in the third
dimension.

The idea of depth, then, can arise in an extremely short time,
and certainly requires no series of movements for its production.
In its case also, that is to say, there must be something among
the peculiarities of vision with the resting eye by means of which
the sense of sight can be freed from the conditions orginally
imposed upon it. This something cannot be anj^thing else than
that whereby our vision of plane surfaces has also been to a
certain extent freed from the co-operation of movements which
orginally were so necessary. Here again the local character
of sensations, which serves to determine their arrangement upon
the retina to which they belong, gives the signal, so to speak,
at which the mind constructs the spatial extension of each
particular retinal image. From the differences which it finds
in these images, it measures the extension of objects in the third
dimension of space. Just as in the areal field of vision the falling
of coincident images upon portions of the retina endowed with a
practically common sensational character gives us an indication
of the extension of the object in a single plane, the excitation
of portions of the retina whose sensations are not of similiar
character serves as a sign for extension in the third dimension.

O

194 Lectures on Human and Animal Psychology

Our measurement of spatial distance corresponding to a certain
difference between sensations was, as you know, originally made
in terms of movement ; but after the measure has once been
obtained, the indissoluble association of the two sensation-series
(sensations of movement and local sensation-qualities) renders
it possible for the first series in certain cases to disappear while
the measure of spatial distance still remains unaffected. At the
same time, observation shows that the connection of the two
series cannot permanently be disturbed without causing a dis-
turbance in spatial vision, and this disturbance can then only be
gradually eliminated by a new serial association term after
term. If, therefore, the eye is freed from the determining
influence of movements in particular perceptions of space, its
freedom is still nothing absolute ; but now and then the renewed
control by movement will be found necessary. Only in this
way is the firm association of the two sensational series, which
are brought into connection with each other by the persistent
operation of conditions seated in the sense-organ, preserved in
undisturbed integrity.

LECTURE XIII

i I. COMBINATION OF SIMILAR STEREOSCOPIC IMAGES. § II. IDEA-
TIONAL CHANGE IN THE COMBINATION OF DIFFERENT IMAGES.
§ III. REFLECTION AND LUSTRE ; THEORY OF LUSTRE. § IV.
PHENOMENA OF SUPPRESSION IN BINOCULAR VISION.

§1

" ¥ " HE fusion of the two retinal images to a single idea is
only a particular instance of a general law of the forma-
tion of ideas. In the visual idea which comes from the two
eyes we do not discover any trace of the perception of one eye
as distinct from that of the other ; but we blend them at once
into a single and indissoluble perception. In this sense it is
true that the two eyes constitute only a single organ of vision.
That they are really like two independent observers, regarding
things from two different points of view, and that we become
acquainted with the properties of objects only by combining the
result of these observations, are facts which we do not remark ;
there is given in consciousness simply the result of this combi-
nation. That is to say, it is not until the two perceptions of
binocular vision have fused that we have an idea ; or, in other
words, the fact that the two eyes unite to perform a common
function is a necessary result of the nature of the mental pro-
cesses of association.

This connection of the separate elements of an association to
a single idea, which is inevitably conditioned by the nature of
the mind, is also furthered by the laws of external perception.
Our external perceptions are of such a character, that they can
only be referred to an object corresponding to the idea which
has been formed of it. So that we can raise the further ques-
tion : how does the ideational activity behave in the presence
of impressions which cannot be referred to one and the same

195

196 Lectiires on Human and Animal Psychology

spatially extended object ? These conditions, of course, are?
never realised in nature; but we can by means of the stereoscope
present to the two eyes impressions of the kind supposed. It
is just as easy to put into the stereoscope different images, chosen
arbitrarily and at random, as it is to bring before the two eyes
in this way the planary projections of one and the same object.
What does the mind do with these perceptions, which it is unable
to combine into a single idea ?

There are scarcely any observations which serve to throw
more light upon the nature of our ideational activity than these
very experiments, in which something is presented to the organs
of sense which is irreconcilable with the laws of their normal
functioning, and which bewilders the mind, as it were, with the
problem of removing the contradiction involved between con-
flicting perceptions. One general law may be formulated :
however great the difference between the separate perceptions
offered to the two eyes, a separate simultaneous apprehension
of them is never possible. What happens is either a combina-
tion of the separate perceptions, on the analogy of stereoscopic
vision proper, or an alternate apprehension of this or that retinal
image.

Wherever the two pictures have a certain resemblance to one
another, — whenever, z>., their difference does not too glaringly
exceed the differences which occur in nature, — they are fused in
a single idea. And even if their differences only correspond
remotely to those shown in the pictures of a tridimensional
object, the idea of depth will still arise at once. The minor
differences are neglected, and the images interpreted in terms
of that class of actual objects which they most closely resemble.

But more than this, figures which cannot be combined at all
to give an idea of depth fuse to a single idea, if they possess a
certain similarity by means of which they can be readily appre-
hended as pictures of the same object. If, e.g., there are placed
in the stereoscope two circles of nearly the same size, there
results the idea of a single circle of mean diameter. In the same
way, if two horizontal lines whose vertical distance from one
another is a little different are presented to each eye, we have as
a result the idea of two lines at the mean distance. Now neither
horizontal lines nor circles of different sizes can give us the idea

Combination of Different Images 197

of depth. How does it happen that their combination is none
the less possible ? We must not forget here that there may be
differences between the retinal images of the two eyes even in
the absence of the conditions necessary for the perception of
depth. If, e.g., we hold the figure of a circle very near our eyes,
but a good deal to one side, — so that the figure is nearer one eye
than the other, — the retinal image of the nearer eye is greater
than that of the more remote, since the magnitude of the retinal
image is directly dependent upon the distance of the object per-
ceived. In this case there are in the two eyes retinal images of
different magnitude ; and yet, when we fixate the circle, we see
it singly. It is just the same with the two horizontal lines, or
with any other figures. So that the condition of vision obtained
by placing in the stereoscope two figures of somewhat different
size is not essentially different from that which sometimes occurs
in normal vision. It is, of course, true that in reality we never
get images of different magnitudes when we fixate an object
lying directly before us, as is the case in the stereoscopic experi-
ment. But that is a secondary circumstance which we may
neglect, because when in normal vision we are estimating the
magnitude of objects lying very far to one side of us we still do
not pay any regard to their different distances from the two eyes.

Quite different phenomena make their appearance if entirely
different objects are presented to the two eyes. If we place in
the stereoscope two pictures representing objects taken quite at
random, we observe a curious alternation of ideas. We neither
perceive two pictures simultaneously and separately, nor do they
fuse together ; but first one and then the other makes its
appearance. It frequently happens that one picture appears by
itself for a time ; then various portions of the other force them-
selves to the front, and then suddenly the second picture alone
can be observed. We notice as a universal rule that there is
never any simultaneous superposition of the parts which belong
to one picture upon corresponding parts of the other ; and that
no complex perception, consisting of parts both of the first and
•of the second image, can hold its place as a permanent idea.

Lectures on Human and Animal Psychology

Such a composite picture is always a transitional stage from one
image to the other. And this transition, or alternation, between
two perceptions forcing themselves upon our consciousness at
the same time, is very readily occasioned by external influences.
In this connection the movement of the eyes is of special
importance. As we move these organs one of them may fixate
some sharply drawn boundary line within the first picture, while
the second is directed upon some less prominent portion of the
second picture. In this way there arises a tendency for the
former to predominate in the resultant idea. But if we again
move the eyes, and this point of fixation changes, the second
image may come to prevail in exactly the same way. First of
all there enters into the idea that portion of the picture which
forces itself upon our notice with special intensity, and this
portion then brings all the rest of the image with it.

FIG. 32.

For the observation of these phenomena we may employ quite
complicated drawings ; but they can be just as well illustrated
by means of simple figures, e.g., by letters of different form. If
we present a U to one eye and a W to the other, or a J to one
and an vS to the other, there is never any fusion to a single idea.
Frequently we see only one letter ; then it breaks up into parts,
and parts of the other letter are added to it ; and, finally, this
latter alone is present in our idea. So that there is no perma-
nence of any one image, but a perpetual alternation, a breaking
down and building up of images ; and the eye is greatly fatigued
by this alternation of images which it cannot control.

If, on the other hand, the two letters have no conflicting charac-
teristics, they may be united in a fairly permanent idea. Thus we
can unite an E and an F, or an L and an F, and in both cases

Reflection and Lustre ; Theory of Lustre 199

obtain the idea of an E. But still the perception is not quite so
steady as is the image of a real E perceived in monocular vision.
When portions of the two images perceived are superimposed
we observe a curious fluctuation in idea. For some little
distance near the boundary the contour is always altogether
interrupted ; and this distance varies from greater to smaller.
A similar interruption of boundary lines may be observed in
the combination of pictures the lines of which cross one another.
If we present to one eye two horizontal lines, A, and to the other
two vertical lines, B, each pair being separated by a moderate
distance (Fig. 32), we obtain a total image in which the lines in
one direction are interrupted by those in the other. It may be
either the horizontal lines, as in C, or the vertical lines, which are
interrupted. This again depends in most cases on the movement
of the eyes. If the point of fixation travels in a vertical direction,
the vertical lines are seen as continuous, and similarly with
the horizontal lines. It seems as if there is a tendency to see
objects in binocular vision as extending in the third dimension,
which has arisen from long habit, and which is manifesting itself
in these experiments. This tendency is realised so far as the
nature of the retinal images permits ; and as a result we simply
see one image behind the other. But the resultant idea is not
completely explained by this supposition. How is it possible for
us wholly to ignore this one set of boundary lines, which is so
definitely presented to us ? How does it happen that portions
of one retinal image completely disappear ?

§ HI

To understand these phenomena, we must familiarise ourselves
with a series of facts, which may be observed both in monocular
and in binocular vision, and which are of not less importance for
the right understanding of the formation of ideas than those
which we have already discussed.

It is a well-known fact that we may see reflected in the
polished surface of a table the ceiling, furniture, and windows of
the room in which it stands. And you all know that not only
are the outlines of the reflected objects perfectly distinct, but the
colours are given quite truly. Natural as this observation
appears, it cannot be directly explained in terms of sensation.

2oo Lectures on Human and Animal Psychology

For if the colour of the table is dark brown, one would have
thought that the white window, mixing with this dark brown,
would produce some shade of light brown. But that is not the
case. The colour of the objects reflected in the table is wholly
unaltered, while at the same time the colour of the table itself is
distinctly seen. We are not able, of course, to apprehend clearly
the colour of the table and the colour of the reflected images
with absolute simultaneity. But we can accurately observe
the two colours in succession without being disturbed by the
mixture of light-impressions on the retina.

Suppose we lay a coloured object, a, upon a uniform colourless
surface, and hold above it a plate of glass, g, placing beside the

glass plate a second object, b, of a
different colour from the first upon a
similar background (Fig. 33). By
looking through the glass plate we see
the object a directly, and in addition
the mirrored image b' of b. That is,
our experiment has exactly repro-
duced by artificial means the con-
ditions which are present in the
reflection of objects in a polished
table ; we see an object, #, of a definite colour, e.g., red, and a
reflected image, b', of an object, b, which is also of a definite
colour, e.g.) white. The result in the two cases is exactly the
same. The image b' is not pale red, but quite unmistakably
pure white ; and if the attention is directed to the object a, it
does not either appear as pale red, but we distinctly cognise it
as a pure red colour. We are, therefore, able to separate out
and to consider in isolation either of the two coloured impres-
sions, in spite of the fact of their intermixture upon the retina.

But this simple experiment is more instructive than observa-
tions of polished tables or other reflecting objects. For in it we
can vary the conditions at will, and so gain more exact informa-
tion regarding the causes of the phenomena. If we turn the sup-
port of b in such a way that it comes to the position c, where it
forms with g the same angle as that formed by the latter with
the support of the object a, the mirrored image of b falls exactly
upon the place where the object a is seen. But now that this

Reflection and Lustre; Theory of Lustre 201

happens, the two images are referred to one and the same distance
in space, and, consequently, fuse together. The result is a
colour-mixture ; the combined image of a and b appears pale
red, so far as the two are superimposed.

The separation of the colours may be prevented in still other
ways. If the coloured objects a and b are not definitely limited,
but are so large that there is no clear perception of their
dimensions, we obtain a mixed sensation, just as in the previous
case where the mirrored image and the image of direct vision
were localised in the same place. But the separation will occur
at once if we draw lines to mark out a smaller figure upon each
of the coloured surfaces. These boundary lines compel us
mentally to assign to each figure its definite distance. And
since the distances of the two figures are clearly apprehended as
different, there arises the idea of a separation of the two
images, with their entire sensation content.

We see here, then, the ideational activity working to effect a
disjunction of impressions such as can never take place in the
sphere of visual sensation proper. In sensation the impressions
are mixed, however different the objects from which they pro-
ceed. But since in the idea every impression is referred to its
object, there is ascribed to each its own amount of participation
in the mixture. Thus the idea corrects, as it were, what is
reported by sensation.

Under certain circumstances, once more, an object may
appear to reflect when seen with both eyes, while it does not do
so for monocular vision. If in Fig. 34 we fixate the object a
with the left eye / alone, we see it in
its natural character. If, on the other
hand, we look at it with the right eye
r, we see the mirrored image b'
behind it. When this image is very
bright and covers the whole of a, it
may happen that the latter is com-
pletely ignored, so that the right eye
sees only b ', and the left eye only a.
As a consequence, there arises the
single idea of a reflecting object, and
with that the clear discrimination of FIG. 34.

2O2 Lectures on Human and Animal Psychology

the object and the image mirrored behind it. Here we have
obviously a case analogous to those already discussed under the
head of stereoscopic experiments. Where the position of the
object corresponds to that of the reflected image, the former is
neglected, just as those portions of one of the stereoscopic
images which were covered by lines of the other image were
ignored. Since our observations of reflecting objects around us
have accustomed us to neglect more or less extensive portions of
an image, we carry this habit of neglecting certain elements into
cases where the objects seen cannot naturally, and without a
forced interpretation, be brought under the head of reflectors.
But this is the sole form of combination whereby the two separate
perceptions can be fused to a single idea.

The phenomena of reflection, which occur both in free and in
stereoscopic vision, are closely allied to those of another class
which are important as throwing considerable light upon the
nature of the ideational activity, — the phenomena of lustre. Lustre
and reflection pass into each other without any very distinct
boundary. Since the phenomenon of reflection depends on an
ideational activity, we may also infer that lustre will be referable
to some mode of ideation. At the same time the popular view
is opposed to such a conclusion. According to it, lustre is at
least something given directly in sensation, if it is not some
quality attaching to the lustrous body as such. But very
simple observations will serve to convince us of the falsity
of this opinion.

We found that when the furniture of a room is mirrored in the
surface of a polished table we are able, despite the mixture of
colours which ensues, to analyse our sensation into its con-
stituents, and that in this way we always cognise the reflected
objects and the reflecting table in their proper colours. But
our cognition of the mirrored objects is only quite clear when
the mirroring surface is very uniformly coloured, so that we
can abstract from this uniform colour of the table surface at the
points where the mirrored images are visible. A good mirror,
however coloured, always shows us the reflected objects just as
they would be if directly fixated. This is not the case if the
mirror is differently coloured in different parts, or if dark and
light places alternate on the polished table. Even though each

Reflection and Lustre ; Theory of Lustre 203

portion of the mirroring surface reflects with equal clearness, the
reflected object is not clearly seen. Why ? Plainly because it
is difficult in such a case to restrict our attention to the appre-
hension of a single object. On the one hand, the attention is
attracted by the boundary lines of the differently coloured
portions of the mirroring surface, and on the other by those of
the reflected object. And this equally strong attraction by
different impressions brings about a conflict of ideas which
prevents any permanent or clear apprehension. We cannot see
the mirrored images clearly for the mirroring object, nor the
mirroring object for the mirrored images. In other cases where
a plurality of ideas is simultaneously presented it is still possible
to apprehend each particular one distinctly by bringing it in
its turn singly before consciousness. Here that is impossible.
For the same sense-organ gives us simultaneously impres-
sions which belong to two different ideas. And, moreover,
the two ideas are of approximately equal intensity, so that
neither the suppression of one by the other nor their alternation
is possible.

The correctness of this account of the origin of lustre may be
confirmed in various ways by experiment The phenomenon of
mirroring obtained when we produce, by means of a plate of
glass, a reflected image behind the place where the object of
direct vision lies, can be readily and immediately transformed
into a phenomenon of lustre by taking the two objects in the
experiments described above (the mirrored object and that
directly fixated) in such a way that the ideas which they arouse
are of equal intensities. Pure mirroring occurs most readily
when the object seen directly is dark, and the mirrored image
bright, and when the former is uniform over its whole surface,
the latter sharply delineated and obviously situated at a definite
•distance behind the real or apparent mirroring surface. Wher-
ever the boundary lines of the reflected image are vague, and
our judgment of its distance accordingly uncertain, or where the
boundary lines of the directly fixated object are prominent and
interfere with those of the reflected image, mirronng passes over
into lustre.

From this it is clear that the phenomenon of lustre will occur
very readily in binocular vision, when one eye sees only the

204 Lectures on Human and Animal Psychology

object, the other only the reflected image. In this case we know
quite well that we have before us two different things, — an object
and an image which is mirrored in the object. In no other way
can it come about that the two eyes perceive different colours.
But we have no idea of the distance of the image behind the
object. We do not even know which of the two perceptions is
referable to object, and which to image. And so a very strong
lustre may be produced by placing in the stereoscope a strip of
coloured paper for one eye and a strip of the same size and
form, but of a different colour, for the other. Green and yellow,
blue and red, or any colours that are sufficiently different, give
an extremely vivid lustre. And in like manner we get lustre
by employing very different degrees of brightness of the same
colour. Strongest of all is the lustre obtained by the com-
bination of black and white. In this case we do not see a
black and a white surface, or a white surface through a black
one, but we obtain the same single impression as when looking
at lustrous graphite or a lustrous metal, except that the lustre
is usually stronger than that which we ordinarily find in natural
objects.

Our every-day experience teaches us that wherever we see
lustre there is no possibility of a clear apprehension of the
objects seen. Too much or too diffuse lustre is therefore un-
pleasant to the eye, though the luminosity of the object be not
nearly strong enough to affect us unpleasantly. A lustrous
stimulus is only pleasant for vision when it occurs at rare
intervals, and allows the sense-organ to recover itself in the
meantime by turning to impressions of the ordinary visual
character. Otherwise lustre dazzles us. And this disturbance
of vision (which may even affect sensation) is again of a mental
or psychophysical character. It makes its appearance wher-
ever there is a conflict of ideas which press upon consciousness
with equal intensity. We have observed its analogue in the
stereoscopic experiments, where pictures differing so greatly
that they could not be combined in a single idea were presented
to the two eyes. In both cases we are only dealing with a par-
ticular consequence of the principle of ideational unity, which
we shall have to refer to again in our discussion of consciousness
and of the connections of ideas in consciousness. While this

Phenomena of Suppression in Binocular Vision 205

principle, in the normal course of our mental life, merely condi-
tions a steady alternation of particular ideas in temporal succes-
sion, it leads to such peculiar phenomena as lustre and ideational
rivalry, when this normal alternation is prevented, whether by
the striving of two ideas for apprehension at the same time, or
by the refusal of a simultaneous plurality of ideas to be resolved
into its elements.

§ IV

In addition to lustre and ideational rivalry, there exists yet
another form of the apprehension of binocular perceptions. If
the perceptions of the two eyes do not press upon consciousness
with equal intensity, but one of them has a considerable pre-
ponderance,— for some reason lying in the nature of the external
impressions, — this predominant impression alone becomes an
idea, while the other is completely ignored. Here again stereo-
scopic experiments enable us artificially to reproduce the condi-
tions of the phenomenon. We can do so most simply by
employing coloured objects of definite outline. If we place a
black background in the stereoscope and lay on this a white
square as an object to be perceived by one eye, we obtain, not
an idea of white and black mixed, despite the fact that the other
eye sees nothing but black, but we imagine that both eyes see a
white square on a black ground ; and the white is as intensive
as that of the object seen with the first eye. That is, the per-
ception of one eye completely suppresses that of the other.
The explanation of this is obviously to be found in the fact that
the definitely outlined white object, contrasting sharply with its
background, possesses a far greater intensity for ideation than
does the uniformly black surface. The same phenomenon may
therefore be observed when we lay a black square upon a white
background, or in general if we present to one eye only a square
of any colour we choose, placed upon a differently coloured
background.

In like manner one perception may be completely changed
by the presence of another if a coloured object of like form and
dimensions is presented to either eye, each, however, contrasting
at a different degree of intensity with the differently coloured

206 Lectures on Human and Animal Psychology

background upon which it lies. Suppose, e.g., that we lay upon
a white background a dark red object for the right eye, and a
dark green object for the left. The perception of the right eye
entirely suppresses that of the left : we see only the red object,
and nothing at all of the green one. If, on the other hand,
we had taken a black background instead of a white one, we
should see only the green object, and nothing of the red. The
reason plainly is, that dark red contrasts with white more
strongly than does bright green, while this latter in its turn con-
trasts more strongly with black. That colour which stands out
more clearly from the background is more intense for ideation,
and so we perceive it alone, and entirely ignore the other. On
a grey background we get the idea of a very lustrous object
seen in greenish light. In this case both perceptions come to
consciousness, because they are of approximately equal inten-
sity, i,e., stand out with equal distinctness from the background.
But, as we have seen, this simultaneous presentation of two
different ideas always gives rise to lustre.

It may sometimes be observed that these phenomena of
suppression do not extend to the entire image, but are restricted
to one part of it. This is especially likely to occur when one
retinal image possesses a much greater extension than the other.

If, e.g., we present
to one eye a white
circular surface, /,
and to the other a
black circle with a
small white spot at
the centre, we shall
FIG. 35- see this last in the

common image as a bright spot surrounded by a very dark
border, which becomes brighter and brighter as we approach
the periphery, and at last almost entirely white. In this case it
is clear that the image r entirely suppresses the image / at the
centre, but conversely is itself suppressed by the latter towards
the periphery, while between these two portions of the common
image there are continuous transition-stages. The following
experiment is of a similar character. To the eye / a uniform
surface, e.g., blue, is presented, and to the eye r two coloured

Phenomena of Suppression in Binocular Vision 207

surfaces, which are joined in the median line, e.g., green and red.
In the common image we see at the centre, where green and
red meet, simply these two colours, while towards the outside
they are intermixed with a bluish colour-tone.

But these two last experiments can only partially be sub-
sumed under the phenomena of suppression. This, it is true,
plays a part in them, inasmuch as a portion of one of the perceived
images preponderates over the other, and thereby causes the
latter to disappear entirely. But the preponderance is in their
case limited to one part of the image, while in other parts of it
it may not infrequently happen, on the contrary, that the image
of the other eye is the predominant one. This fact seems to be
almost directly opposed to the laws of ideational activity. The
fact of the unity of the idea we have seen to be firmly estab-
lished. It is no contradiction of this that one perception per-
manently suppresses the other, or that two perceptions alternate
in succession ; but that each of the two perceptions should be
partially apprehended, and so appear in ideation in the form of
a mixed image, — this seems to be scarcely in harmony with our
law. We have, however, already become acquainted with a
whole class of phenomena in which also two perceptions may
combine to form a single idea : these, as you know, are the
phenomena of lustre and reflection. In the case of lustre two
ideas are presented to us, which we do not succeed in keeping
separate. In mirroring we effect this separation, and we can
therefore either alternate between the idea of the reflected and
that of the reflecting object, or we can unite both of them in a
total idea. When we look at the image in a mirror, we usually
embrace both image and mirror in a single idea ; the mirror is
the frame which surrounds the picture. Now in the experiments
which we have just been describing we have obviously the same
conditions. Besides the considerable intensification of one por-
tion of a visual perception, the idea of reflection also exerts
some influence. And therefore that especially prominent por-
tion of the perception of one eye is alone given in ideation at
the place which it occupies in the common image, at the other
parts of which ideation has free play, and so tends to apprehend
the image of the other eye as a mirror in which the first is seen.

Still the conditions in this artificial experiment do not entirely

2o8 Lectures on Human and Animal Psychology

correspond to what takes place in nature. In nature, too, it
may happen that we see only the mirror with one eye, and only
the mirrored object with the other. We need simply hold the
mirror close to our eyes and cause the mirrored image to fall
very much to one side. But there are many conditions which
we can introduce into the experiment which are never realised
in nature. Suppose, e.g., that we place a large blue and a small
yellow object in the stereoscope for combination in binocular

vision, both lying on a red

Blnw

background (Fig. 36) ; we have
a common image, in which the
yellow is seen surrounded by
blue. ' So far there is nothing
out of the common, for it may
also happen in nature that we
see a yellow object reflected in
a blue mirror. But where this

happens we must necessarily see the mirror with the same eye
which sees also the mirrored object. For if we are viewing a
small object in a very large mirror, it may certainly happen that
this image is only visible to one eye, but the mirror itself is
never visible to one eye only, least of all to the one which is
not looking at the mirrored image. The conditions of the
experiment here, then, are not in accordance with nature. How
does the eye cope with its perplexity ? Since the right eye sees
yellow upon a red background, and the left blue on the same,
there is occasioned simply the idea that a yellow object on a red
background is mirrored in a blue object ; that is, not only the
yellow object, but also the red background which immediately
surrounds it, are comprehended in the resultant image. Farther
towards the lateral parts of the image, however, there arises in
ideation the perception of a blue surface distinctly outlined
against the red ; and so the blue sensation gradually comes to
predominate. Thus we obtain as a final image that of a large
blue square upon a red background, in the middle of which is a
small yellow square surrounded by a fringe that shows a deep
red on the inside, but becomes more and more tinged with blue
towards the outside.

All these phenomena, which can be varied in many other

Phenomena of Suppression in Binocular Vision 209

ways, show that a single idea is always formed from the percep-
tions of binocular vision, and that this always takes place on the
analogy of the conditions of vision found in nature. The pro-
cess by which the two visual perceptions unite to form one idea
depends, therefore, upon the formation of numerous associations,
some acting in harmony with, and some in opposition to, one
another. In this latter case, phenomena of suppression, or idea-
tional rivalry, make their appearance. The separate perceptions
of the two eyes are themselves composed of sensations which
combine with each other in a quite different way from the light-
impressions which fall upon one retinal point in the same eye.
We have rather to regard the binocular visual idea as a mental
resultant of the originally separate perceptions of the tzvo eyes.

LECTURE XIV

§ I. THE FEELINGS. § II. SENSE-FEELINGS. § III. COMMON FEELING
AND THE OTHER TOTAL FEELINGS. § IV. RELATION OF FEELING
TO IDEA.

§1

THE mental phenomena with which we have been con-
cerned hitherto have represented stages in one and the
same great process. We have seen that ideas are derived from
sensations in the regular course of development, and that both
alike have a single end, — knowledge of the external world. But
we have purposely neglected one very important side of our
mental life. We never actually find a mind which apprehends
things without joy or sorrow, and contemplates them with ab-
solute indifference. In cognising objects we feel ourselves
attracted to or repelled from them, or incited to the performance
of some kind of action, according to their nature. We can,
therefore, comprehend all those phenomena which are not in-
cluded in the ideational process under the two words 'feeling' and
'will.' Feeling and conation always accompany our sensations
and ideas ; they determine our actions, and it is mainly from
them that our whole mental life receives its bias and stamp of
individuality.

Feeling and will are closely interconnected. And both are
again connected with ideas. The separation between these
processes is one that exists only in psychological abstraction,
and has no basis in reality. Feeling passes over into impulse,
impulse into voluntary action, and voluntary action has reference
to objects which are given to us as ideas.

In ordinary language we employ the word ' feeling ' in
various senses. We call hunger and thirst ' feelings ' ; we speak
of the ' feeling ' of pain, and of ' feeling ' external objects

The Feelings 211

with our hands ; we call love and hate, joy and sorrow, hope
and anxiety, ' feelings ' ; we talk of our ' feeling ' for the
beautiful and the ugly, and even of ' feeling ' that something is
true, or honourable, or virtuous. What is our justification for
bringing under one and the same concept mental processes
which are so diverse in their nature, and belong to such different
stages of development ? It may be mere chance ; language
may somehow have come to apply the same name to a number
of totally different phenomena. Or it may be purpose ; perhaps
these processes possess something in common, notwithstanding
all their divergences.

As a matter of fact, there is one point in which all ' feelings '
agree, however different they may be in other respects : they
all imply a condition of the feeling subject, an affection or
activity of the self. Feelings are always subjective, while the
idea always has an objective reference. Even when the matter
of ideation is some one of our own conscious processes, this
is regarded objectively. So that the term 'sense of feeling'
has been reserved for the sense whose impressions are most
obviously connected with subjective states of pleasure and un-
pleasantness. What language implies in calling joy and care,
love and hatred, 'feelings/ is simply that they are apprehended
as exclusively subjective states, and not as properties of objects
outside us.

The attempt has sometimes been made to limit the meaning
of the term ' feeling,' on the ground that the processes compre-
hended under it are entirely too diverse in character. And in
particular it has been thought necessary, from the psychological
standpoint, to strike out from the category of feeling all those
subjective excitations which are directly connected with sen-
sations. Hunger, thirst, bodily pain, impressions of touch in
general, are, it is said, sensations ; they are accompanied by
physical processes in the nervous system : but feeling is a purely
mental condition. The term should, therefore, be confined to
mental states which are independent of bodily affections and
arise solely from some kind of reciprocal action among ideas.
But as soon as we give up the* reference of feeling to a subjec-
tive condition of pleasure-pain, or of some similar pair of sub-
jective opposites, we have no reason for uniting affective states

212 Lectures on Human and Animal Psychology

in general in a common class. If, on the other hand, we retain
this principle of classification, we cannot exclude from ' feel-
ing' the sense-feelings attending the simple sensations. It
seems to have been regarded as a difficulty that one and the
same simple process should be called both sensation and feel-
ing. But it has been forgotten that joy and sorrow, hope and
anxiety, and all the other ' feelings ' are really states of mind
which are affective only so far as they have reference to the
feeling subject ; while in other respects they depend upon ideas
which objectively regarded are entirely empty of feeling. The
only difference is, that in the case of these more complex feel-
ings we attach a greater value to the feeling as such, and
therefore give a separate name to each of its particular forms.
A very complex ideational association may give rise to a feel-
ing which is simple and uniform throughout. We are, therefore,
inclined to substitute the subjective result, the feeling, for those
various and complex processes which serve as its objective
background. There is no need for this in the case of the simple
sense-feeling. Its objective substrate is a sensation which is
equally simple with it, and more readily discriminated by virtue
of its relation to an external object.

If the feeling is characterised merely by its relation to the
feeling subject, it is clear that the distinction between it and
the sensation or idea cannot be in any sense original. The
simple sense-feeling in particular is contained in the sensation ;
and it is just as incorrect to say, ' Feelings alone are primitive,'
as to say, ' We have at first simply sensations.' The ultimate
fact is, that we sense and feel. The logical separation of
feeling from sensation can only come about after we have dis-
tinguished subject from object. Then, and then only, is the
elementary process of sensation analysed into a subjective factor,
the feeling, and into an objective factor, the sensation. The
sense-feeling may in this way be considered as an integral
element of the sensation itself; and for that reason it is also
termed the affective tone of sensation.

Since the aim of these lectures is to give a general description
of the elementary constituents of our mental life before dealing
with their connection in consciousness, and the complex pro-
cesses to which this connection gives rise, it will be best for us

Sense- fee lings 213

to confine our attention here to the sense-feelings. The simpli-
city of the conditions upon which they depend makes it easy
to examine them without any detailed reference to their con-
nection in consciousness. For the same reason they will giv%
us the most efficient aid in our endeavour to understand the
general nature of feeling and its relation to will. But we shall
be obliged occasionally to glance at the higher feelings, —
especially the intellectual and aesthetic. There are certain
problems to which these furnish more definite answers, just
because of the more complex associations which they involve.

§ II '

There are some sense-organs which require quite intensive
stimulation for the production of a sense-feeling possessing any
considerable degree of strength. This is especially true of the
eye and the ear. A moderate visual or auditory stimulus seems
to give rise to scarcely anything except the objective sensation ;
a moderate light-impression, e.g., is referred simply and solely
to the external illuminating object. But it must be admitted
that careful introspection enables us to recognise a certain
affective tone even in the sensations produced by weak visual
and auditory stimuli. We notice this especially when the im-
pressions are given without direct reference to external objects
with clearly defined boundaries. Thus the different spectral
colours, — red, green, blue, etc., — as well as white and black, have
characteristic, if weak, feelings attaching to them ; while every
single musical clang is also attended by an affective tone, deter-
mined in each case by tonal pitch and clang -character. But
the intensity of these feelings is very slight Their importance
is, however, increased by the fact that they enter as intensifying
elements into the cesthetic feelings, which are more elaborate
affective states, connected with entire ideational complexes.
On the other hand, a dazzling light or a deafening sound will
directly occasion a feeling of pain, behind which the objective
significance of the sensation may in its turn entirely disappear.
These intensive stimuli disturb the normal functioning of the
organ ; and it is, therefore, the subjective factor which comes
most predominantly into consciousness.

214 Lectures on Hitman and Animal Psychology

Cutaneous sensations are also as a rule referred wholly to
external impressions, so long as they are not painful. But there
are certain stimuli which, although truly tactual, produce sen-
Nations with very intensive affective tones. Stimuli of quite
weak intensity, which only lightly touch the surface of the
skin, excite tickling or itching. Both of these may also arise
independently of external impressions. They are always charac-
terised by a tendency to diffusion of effect. The mechanism
of the matter probably is that weak tactual stimuli call into
reflex activity the unstriated muscles which lie directly beneath
the skin, and to which cutaneous movement is due. When
these muscles are contracted, we have also the peculiar feeling
of shivering accompanying the muscle-sensation proper ; and
this readily combines with the feeling of tickling. The reflex
excitation of the cutaneous muscles frequently extends to
other muscle groups ; and when the excitability is great, may
lead to general reflex convulsions, which are greatly exhausting
to the organism.

A fairly low degree of temperature has an analogous result.
If we let a cold stimulus of slight intensity act upon the skin,
we have first a sensation of cold, — i.e., the cold is perceived as
an alteration in the condition of excitation of the cutaneous
organs, — then the smaller cutaneous muscles are reflexly excited,
and so the feeling of shivering is occasioned. The same effect
may be produced by the action of internal causes in producing
a sudden loss of heat, and consequently a cutaneous sensation
of cold. This happens in fever chills, where the effect is much
intensified by the abnormal reflex excitability of the cutaneous
muscles. Very high or very low temperatures, finally, have the
same result as very strong pressure-stimuli : they do not pro-
duce sensations of heat or cold, but only severe pain. And
it is of the very nature of pain that its character is always
constant : a prick, a grinding pressure, intense heat, and freezing
cold all excite pain of the same strongly affective quality.

It is different with impressions of smell and taste. Even at
weak intensities, these are accompanied by distinct feelings of
pleasure and unpleasantness. And the feeling is so closely
fused with the sensation that it seems impossible to think of
the two as even temporarily dissociated. It is only the fact

Sense-feelings 215

that there are impressions which are relatively free from feeling
which leads us to believe that the quality and intensity of the
feeling depend upon other conditions than those of the sensa-
tion. It is, perhaps, scarcely necessary to point out how
important the strong affective tone of the sensations of smell
and taste is for our physical life. Here, more than in any of
the other senses, the feelings of pleasure and pain serve as sub-
jective indications of the impressions which we should seek
and of those which we should avoid. These indications may, of
course, occasionally lead us astray ; but the adaptation of
natural unperverted feeling to the beneficial or injurious charac-
ter of stimuli is on the whole marvellously complete.

But peripherally excited sensations do not constitute the
only material for the formation of sense-feelings. There are a
large number of sensations which are not caused by external
impressions, and which do not imply the apprehension of ex-
ternal objects, but which may in all other respects be co-ordi-
nated with the sensations from the sense-organs proper. To this
group belong, in the first place, the muscle-sensations, which we
have already described in our inquiry into the processes con-
cerned in perception. Moderate muscular exercise is connected
with a more or less distinct feeling of pleasure ; while ex-
haustion, excessive effort, or a pathological condition of the
muscles not only alters the quality of muscular sensation, but
also brings with it a very intensive feeling of unpleasantness.
Secondly, there belong to this class sensations from the various
tissues and organs of our body. These are generally of slight
intensity, and therefore easily overlooked. But under special
conditions, especially where the state of the particular organ
or tissue is pathological, they may become so intensive that
the feelings connected with them dominate consciousness
almost exclusively, and produce general discomfort throughout
the organism. These sensations, therefore, are only familiar to
us at their highest degree of intensity, i.e., when they have be-
come painful. But the affective character of pain is, as we have
already remarked, essentially the same in every case. For that
reason, the specific differences of the organic feelings are not
generally apprehended by us. Nevertheless, observation shows
that such specific differences really exist. Language uses

216 Lectures on Human and Animal Psychology

different terms to denote the pains coming from different
organs. We speak of ' stabbing ' and ' gnawing ' pains in our
bones, of 'pricking' pains in the porous serous membranes,
and of ' burning ' pains in the mucous membrane. Here,
as in the external sense-organs, pain is simply the sen-
sation raised to its highest degree of intensity ; and that
peculiar property of the pain which is dependent upon the
structure of the organ is prefigured in the pure sensation. This
is especially noticeable in intermittent pains. There are times
when sensation is present which cannot be called painful; and
during these intermissions the peculiar sensation-colouring
which gives its special character to the ensuing pain is usually
not at all affected.

We may, therefore, regard these sensations from the bodily
tissues and organs as originally equal in value to those from
the organs of special sense. Gradually, however, these latter
acquire a paramount position, through their importance for the
development of ideas ; while the great majority of the organic
sensations pass unnoticed until their unusual intensity in a
particular case announces some important change in the con-
dition of the organism, of which consciousness is obliged to take
account. That is to say, in proportion as sensations, originally
given as. undifferentiated, are divided up into sensations of
special sense (relatively free from affective tone) and organic
sensations (strong in affective tone), there is a tendency for this
latter group gradually to disappear from consciousness. Hence
the entire life and action of the child is determined by the
sense-feelings ; while the more developed and better furnished
the mind becomes, the more independent is it of their domina-
tion, and the greater is its measure of success in permanently
repressing the weaker sense-feelings and at least temporarily
subduing the stronger ones. The only exception is the hypo-
chondriac, who delights in observing his own bodily symptoms
and states. By dwelling anxiously upon all those weak sensa-
tions which pass unnoticed by the normal consciousness, he
gains a great deal of training in the apprehension of his sense-
feelings. The physician will often laugh at his ' pains ' and
'aches' as illusions ; but generally they are real enough. The
abnormality of the hypochondriac does not consist in his per-

Common Feeling and the Other Total Feelings 2 1 7

ception of feelings which have no existence, but in his distinct
apprehension1 of, and anxious reflection upon, feelings which a
healthy man usually takes no notice of.

To the specifically organic feelings belong also those of
hunger, thirst, and shortness of breath. They, too, are con-
nected with sensations which normally recur with moderate in-
tensity at definite intervals, but which will increase more and
more in affective intensity, if their demands are not satisfied.
Hunger,, thirst, and respiratory excitations are sensations cen-
trally aroused, but peripherally localised, — thirst in the mucous
membrane of the palate and throat ; hunger in the stomach ; the
respiratory sensations in the respiratory organs, and especially
in the muscles of the chest, which subserve the process of
breathing.

§ HI

Our general condition of bodily comfort or discomfort is de-
pendent upon the mass of organic sensations which are always
present, but in varying degrees of affective intensity. The
totality of feelings acting upon consciousness at a given moment
is termed the common feeling. This has been defined in terms
of its origin as the sum total of simultaneously present organic
feelings of whatever quality. But the definition overlooks the
fact that our state of feeling is always qualitatively single. We
can never be moved simultaneously by a number of diverse and
independent feelings ; they combine to form a resultant possess-
ing the character of a feeling of definite quality and intensity.
At a given moment we feel 'well,' or 'ill,' or indifferently. If we
should ever say, in speaking of our general bodily condition,
that we are feeling at once ' well ' and ' ill,' it may always be
proved by introspection that we have been uniting successive
feelings in the single judgment. But this is the result of re-
flection upon our feelings ; the fusion is not given in the feelings
themselves.

This qualitative unity of feeling seems to correspond to the
ideational unity of our consciousness. The sensations excited
at a given moment by external and internal stimuli are not
perceived as a mere medley of impressions, but are associated to
form ideas, which are then brought into spatial and temporal

relations with each other. In the same way all the particular
feelings are united in one total feeling, into which each enters
as a constituent factor. But the analogy cannot be carried any
farther ; there is an important difference between the two pro-
cesses. We can prove that an idea is a compound process by
analysing it into sensations. A clang, a compound clang, and
a visual object are single, but not simple, mental facts. We
can analyse each of them into a number of simple sensation-
elements. But no feeling is capable of analysis in introspection,
whether it is connected, like the sense-feeling, with a single
sensation, or, like the elementary aesthetic, intellectual, and
moral feelings, with a complex ideational group.

This simplicity of feeling, together with its subjective charac-
ter, which makes it impossible for us to refer it in every case to
external objects, as we do with sensations and ideas, is doubtless
the cause of that ' obscurity ' which has been so often empha-
sised, and which consists simply in the indefinable nature of
affective quality. It is this ' obscurity ' which has led to the
attempt to substitute for the impossible definition an enumera-
tion of the objective conditions under which feeling arises, and
a description of the relations obtaining between the ideas pre-
sent at the moment of its appearance. These supply the only
means at our disposal for the production in others of feelings
similar to those which we experience ourselves under particular
circumstances ; and they are perfectly justifiable so long as we
do not mistake them for an account of feeling itself. But
psychology has fallen into this very error again and again.
That is, it has ' explained ' feeling by reflecting upon the ideas
among which it arises, and by which it is attended. Sense-
feeling has been defined as a furtherance or inhibition of our
bodily well-being, or even as a direct cognition of the useful-
ness or danger of sense-stimuli. Esthetic feeling has been said
to consist in the idea of definite mathematical proportions,
moral feeling in reflection upon the useful or hurtful conse-
quences of our actions, and so on. Leaving out of account the
objections to these theories on other grounds, we see that they
are all overthrown by the consideration that feeling is not it-
self an intellectual process at all, although it is always con-
nected with intellectual processes

Common Feeling and the Other Total Feelings 2 1 9

Every feeling is a qualitatively simple and undecomposable
mental state. This fact does not, of course, exclude the possi-
bility of there being in consciousness several simultaneous feel-
ings. Only, these simultaneous feelings always combine in a
total feeling which possesses a unitary character, and cannot,
therefore, be regarded simply as the sum of the original par-
ticular feelings. The oscillatory and the discordant feelings are,_
perhaps, the most instructive examples of these complex affec-
tive states. In the first group, opposing feelings alternate with
each other in rapid succession. But there is also a continuous
modification of one affective phase by the other, so that a new
feeling with a characteristic quality of its own arises alongside
of the primary changing feelings. Its quality is, of course, de-
pendent upon those of the original feelings ; but it cannot be
analysed into them. Its intensity is constantly altering, so that
at one moment the primary feelings, at another this new per-
manent feeling which is characteristic of affective oscillation,
predominates in consciousness. Affective discordancy is directly
derived from affective oscillation. It occurs when the oscilla-
tions of feeling follow each other very quickly, and the successive
feelings themselves are strongly opposed. We have an ex-
ample of this from the sense-feelings in tickling, and from
the intellectual feelings in doubt ; while the dissonance of
two clangs may be taken to exemplify it in the field of the
elementary aesthetic feelings.

The statement that doubt is a compound of the feelings of
acquiescence and repugnance is certainly a true description
of the alternating affective states which go to constitute the
entire mental process. But there seems to be present in addi-
tion a resultant total feeling directly corresponding to the dis-
sension in the emotional condition. There may be moments of
doubt when neither the feeling of acquiescence nor the feeling
of repugnance is in consciousness at all ; and these moments
possess a unique affective character which does not appear to be
analysable into either of the other two feelings which displace
it from time to time ; but it may continue to exist alongside
of them. At such moments, therefore, there exist three feel-
ings,— those of acquiescence and repugnance and the total feeling
resulting from the two, but qualitatively different from them.

220 Lectures on Human and Animal Psychology

Doubt always involves a strong opposition between the con-
stituent feelings. In the feelings of tickling and of dissonance,
which are formally related to it as ' discordant ' feelings, although
their ideational connections are entirely different, the affective
state is more homogeneous. In tickling, which is due to a con-
tinued weak cutaneous stimulation, we can clearly distinguish
two original feelings, either of which may predominate accord-
ing to circumstances, — a pleasurable feeling, which probably
accompanies the weak touch-sensations ; and a painful feeling,
which appears to be connected with reflexly excited muscle-
sensations, to which, e.g., those of the diaphragm belong. If the
tickling is slight, the direct effect of the stimulus, and therefore
the pleasurable feeling, is most prominent ; if it is more inten-
sive, the reflex effect, and therefore the unpleasant feeling, gains
the upper hand. The specific total feeling of tickling is the
resultant of these two. It, again, may be perceived with especial
clearness when the two opposing factors are of approximately
equal intensity. But in general, and perhaps as a result of the
strength of the two factors, the total feeling in tickling is of
relatively slight intensity. The opposite holds of the dissonance
of two clangs, when we can always distinguish the feelings which
are connected with the separate clangs from the total feeling of
dissonance, itself. As the dissonance increases, the total feeling
prevails more and more over those excited by the separate
clangs.

We see, then, that the total feelings arise from the union of
particular feelings, but that they constitute new and simple
feelings of definite quality, quite distinct from their constituents.
Plainly the common feeling must be regarded as belonging to
this group. We do not intend to denote by the phrase the
medley of miscellaneous separate feelings present in conscious-
ness at a given moment, but rather a new feeling to which they
give rise, and whose quality they all help to determine. The
entire sum of separate feelings combines to form a complex
unity, the trend of which finds its expression in the resultant
total feeling. Similar total feelings with accompanying par-
ticular feelings constitute the ' higher ' intellectual, aesthetic, and
moral feelings. In all these cases, every particular feeling and
every total feeling have their own characteristic quality, in

Relation of Feeling to Idea 221

virtue of which they stand in relations of agreement and dis-
agreement to other feelings, though they are never analysable
into them. So that nothing can be more erroneous than the
opinion sometimes held that the entire world of feeling is com-
posed of a certain sum of elementary feelings, — perhaps sense-
feelings, — of approximately constant quality. The essential
characteristic of feeling, especially of the higher feelings, is
rather an inexhaustible wealth of qualities ; new qualities arise
from the mutual influences of simultaneous feelings, and from
the induction of present by antecedent feelings. And to this
we must add that the worth of the feelings constantly increases
as the relations in which they stand become more complex, for
it is these relations which determine the influence of any par-
ticular feeling upon our entire mental life.

§ IV

Finally, the existence of total feelings, and especially of those
which reflect an oscillatory or discordant affective state, leads
us to an important fact, without mention of which everything
that we have said about feeling, and especially about the origin
of resultant feelings, would be incomplete. We have considered
feeling primarily as a process which accompanies ideation.
Since we have been occupied hitherto with the analysis of ideas,
they naturally suggest themselves as points of departure for our
investigation of feeling. But ideas are not the only mental
processes, even if we abstract from feelings and the other sub-
jective processes connected with them. All the changes which
occur in a given ideational content are as such also mental
processes characterised by a particular rapidity and manner of
occurrence, and, like the ideas themselves, connected with feel-
ings. So that even from the standpoint of an objective obser-
vation, which only takes account of the ideational, and not of
the affective, side of mind, we are obliged to distinguish these
processes of change in ideational content from the ideas which
are altered. Introspection of such changes is also sometimes
called ' ideation.' We are told, e.g., to ' form an idea ' of some
change ; that a content is appearing or vanishing, or that con-
tents are passing through consciousness with greater or less

222 Lectures on Human and Animal Psychology

rapidity. It is scarcely necessary to remark that we are not
really dealing here with two different things, — ideas and changes
in their condition and arrangement. The analogy with physical
bodies and their changes of position which is usually thought of
is entirely misleading. The ideas themselves are, as you know,
not unchanging objects, but processes, occurrences, whose exist-
ence is necessarily bound up with that of the changes supposed
to take place in them. If, e.g., an idea disappears, that means
that the mental process which we call an idea ceases to exist.
So that when we speak of ' ideas with which feelings are con-
nected ' our language is at least subject to misinterpretation.
We should rather say : all ideational processes, whatever their
nature, whether they consist of the idea of an external object,
or of some internal change in this idea, are at the same time
affective processes. Affective discordancy furnishes an obvious
proof of this : in doubt and in dissonance the resulting feeling
is determined to a far greater extent by the characteristic
alternation of ideas than by the nature of the ideas themselves.
The total feelings in particular are always essentially dependent
on some peculiarity of the alternation and succession of ideas.
We shall return again to this point in our consideration of the
emotions, of which total feelings are important constituents.

LECTURE XV

§ I. RELATION OF FEELING TO WILL; IMPULSE AND DESIRE. § II.
DEVELOPMENT OF WILL. § III. SIMPLE AND COMPLEX VOLUNTARY
ACTS. § IV. PSYCHOLOGICAL ELEMENTS IN VOLUNTARY ACTION.

§ I

IN the previous discussion we took as our starting-point the
fact that the affective side of consciousness at any moment
seems to exhibit a unitary interconnection similar to that
presented by its ideational contents. But further investigation
convinced us that the affective unity of consciousness differs in
important respects from its ideational unity. The latter appears
to be external, in the sense that the particular ideas are united
into a whole, more especially by the spatial relations in which
they stand to each other, without the constituents of this whole
being necessarily brought into any internal relation. In feeling
it is quite different. It is true that several qualitatively different
feelings may exist side by side, but they always give rise also to
a total feeling which endows the entire group of separate feelings
with an internal coherence.

We shall best understand this internal unity of feeling if we
look somewhat more closely at the connection of feeling with
will, — a subject to which we referred in a general way at the
beginning of the last lecture. This connection may be regarded
from two points of view. In the first place, feeling is only
thinkable as a mental state of a being endowed with will ;
pleasurable and unpleasurable feelings tend to direct the course
of the will. Whether or not they pass over into actual volition
is determined by internal and external conditions. But without
the capacity to will the alternatives could not possibly exist.
Secondly, will is an internal process, distinguished from other

224 Lectures on Human and Animal Psychology

mental activities through the fact that in it we are conscious of
definite motives. But motives are always accompanied by feel-
ings, and the feelings further appear to us as those elements of the
motive which contain the real reason for the activity. Without
the excitation which feeling furnishes we should never will any-
thing. A mind which contemplated things with entire indiffer-
ence as ' pure intelligence ' could never possibly be roused by
them to volition or action. Feeling, therefore, presupposes will,
and will feeling. In a concrete voluntary action the two are
not different processes, but part-phenomena of one and the same
process, which begins with an affective excitation, and passes
over into an act of will. It often happens, however, that the
final term in this series is wanting : the intensity of a feeling
may become lessened, or it may be displaced by another feeling
without leading to an act of will. We may therefore divide
feelings at once into two groups, — those which form constituents
of a voluntary act and those from which no definite volition
results. The latter class, again, contains different degrees. If
the subjective condition is, and remains, simply a pleasant or un-
pleasant mood, we speak of a feeling proper. When there is
added to this a definite tendency towards a willed result, we
term the internal process an effort or an impulse. If in this
effort we are further conscious of some inhibition, which prevents
it from passing over directly into volition, we call it a desire.

It is in the doctrine of feeling and will more than anywhere
else that psychology still wears the fetters of the old faculty
theory. And so it has usually taken a radically false view of
these intimately connected part-processes, regarding each con-
stituent as an independently existing whole, which might in-
cidentally, but need not necessarily, exert an influence upon the
constituents of the other. Thus first of all feeling was con-
sidered apart from its connection with will, and then desire was
treated as a separate process, sometimes found in connection
with feeling. Further, impulse was opposed to desire proper as
an obscure desire, in which the subject is not conscious of the
desired object ; or, perhaps, as a lower desire, referring exclusively

Development of Will 225

to the needs of sense. (That is why many psychologists hold
that impulses only exist among animals.) And finally these
processes are still further supplemented by the postulation of
will as an entirely new and independent faculty, whose function
it is to choose between the various objects of desire, or in certain
circumstances to act in accordance with purely intellectual
motives and in opposition to impulses and desires. According
to this theory, that is, will consists in the capacity for free
choice. Choice in this sense presupposes the possibility of
decision between various objects of desire, and even of decision
against the desired object on the ground of purely rational con-
siderations. It was therefore supposed that desire is a condition
which precedes volition, and that at least in many cases this
latter is only the realisation of desire in action.

We must pronounce this theory a purely imaginary construc-
tion from beginning to end. It has taken its facts from every
possible source except an unprejudiced, introspection. Feeling
is not independent of volition, as alleged ; impulse is not a
process which can be distinguished from will, still less opposed
to it ; and desire is not the uniform antecedent of will, but
rather a process which only appears in consciousness when
some inhibition of voluntary activity prevents the realisation of
volition proper. Finally, to define the will as the capacity of
choice is to render any explanation of it impossible from the
outset. Such a capacity presupposes volition as its antecedent
condition. If we could not will without choice, — i.e., as directly
determined by internal motives, — a volition involving choice
would necessarily remain impossible.

This confusion of volition and choice brings another error in
its train. Will is supposed to arise from all sorts of involuntary
activities. Generally this view is applied exclusively to external
voluntary acts, which many psychologists regard as the only
ones. Both the human and animal body, it is said, were
originally, before the appearance of will, the seat of reflex move-
ments of the most diverse character. These were for the most
part purposive, owing to the teleological connection of sensory
with motor fibres in the central organs. Thus a stimulus which
caused pain would give rise to a reflex movement of defence,
resulting in the removal of the stimulus. It is further supposed

Q

226 Lectures on Human and Animal Psychology

that the mind perceives the purposiveness of these reflex re-
actions, and so the thought arises in it that it might possibly
undertake similar movements itself, and attain the same pur-
posive result. The next time that the stimulus approaches,
therefore, the mind will be on the sjert to execute the defensive
movement, and so remove the stimulus before it has any painful
consequences. The most remarkable results of this kind of re-
flection are those obtained as regards locomotion. It may per-
haps happen that the body gives a sudden spring, in response to
a strong reflex stimulus. ' Eureka ! ' says the mind to itself.
' Why should I not cause my body to spring when this un-
desirable stimulus is not there?' But when the will has once
discovered that its voluntary muscles enable it to do almost any-
thing it wishes, it, and not the reflex, is master. The reflex has
played its part, and is henceforth restricted to the sphere of the
absolutely necessary.

You will not find, of course, that this description is in literal
agreement with that given in any of the works treating of the
development of voluntary acts from reflex movements, but in
substance there is no difference. You will even find such ex-
pressions as ' The mind takes note of this and that,' or ' It now
executes movements voluntarily which it formerly observed
taking place in the body involuntarily.' And indeed there is no
reason why the mind should not act in this way, if it were '' pure
intelligence,' as these writers palpably assume, or even if it
only had at its disposal a small number of feelings to occupy
its leisure moments.

But the matter assumes a different aspect when we look at it
without preconceptions, and refrain from reading into the facts
of observation notions and reflections which exist only in our
own minds. In the first place, there is not the slightest con-
firmation to be found for the assertion that the lower animals,
and children in the early days of life, are merely reflex machines,
which make certain movements with mechanical certainty as
soon as we press the spring. Even such of the protozoa as un-
doubtedly belong to the animal kingdom give plain evidence of
voluntary movement. The chick just out of the shell executes
movements which are in great part at least of the nature of
voluntary actions. No one will of course deny that reflex

Development of Will 227

movements may also be observed from the first especially
among the more complexly organised animals. We have our-
selves referred to the reflex movements of the eye and the
organs of touch, and the part which they probably play in the
formation of our space-perceptions (pp. 126 ff.). It must not,
however, be forgotten that these purposive reflexes have become
possible through an organisation acquired in the course of count-
less generations. What are the conditions which have been
operative during this development to increasingly modify the
organisation of the nervous system, so that the movements
which constitute its mechanical response to external stimuli may
be as well adapted as possible to subserve the immediate ends
of the life of the organism ? There is only one intelligible
answer to this question. It consists in a reference to those
processes which even during the individual life mediate the for-
mation of purposive reflex and automatic movements, to the
processes underlying practice. Practice always implies that an
action which at first was performed voluntarily has gradually
become reflex and automatic. Thus when the child learns to
walk, the taking of each single step is accompanied by a consider-
able effort of will ; but after a time and by slow degrees it be-
comes able to initiate a whole series of movements without
attending to their execution in detail. In the same way, we
learn to play the pianoforte or to execute other complicated
movements of the hands by frequent repetition of particular and
connected acts, and their consequent transformation into a chain
of effects which follow each other with mechanical certainty
when once the appropriate impulse has been given. Now the
modifications which the nervous system undergoes during the
life of the individual in consequence of the mechanising of these
practised movements must naturally, like all other modifications
of the same kind, be summated and intensified in the course of
generations. The purposive character of the reflexes becomes
then readily intelligible, if we regard them as resulting from the
voluntary action of previous generations ; while, on the contrary,
the view which sees in them the starting-point of the will's
development fails to explain their existence and purposiveness,
and is further in disagreement with the results of objective and
subjective observation, — with objective : for the observation of

228 Lectitres on Human and Animal Psychology

animals, and especially of the lower forms of animal life, never
goes to prove the primitive character of reflexes which the
theory assumes; and with subjective: for it remains com-
pletely unintelligible how a decision of will can arise from purely
intellectual processes. Introspection invariably points to feeling
as the antecedent of will ; but feeling, as we saw above, is not
separable from it, since it always implies a certain tendency to
will in one way or the other.

Moreover, this theory usually occupies itself exclusively with
external voluntary actions, and entirely overlooks the fact that
there is an internal volition manifesting itself only in the form
of conscious processes. We direct our attention voluntarily
upon any object which appears in our field of vision ; we are
clearly conscious of an effort of will in trying to recall a word or
a fact that we have forgotten. We voluntarily turn our thoughts
in different directions in selecting out of a number of ideas
which are passing through consciousness those which have most
direct reference to the general trend of our thinking at the time.
It is quite impossible to derive these internal voluntary processes
from external voluntary actions. It is surely obvious that the
contrary is true, — that every external voluntary act presupposes
an internal volition. Before we voluntarily execute any particular
movement, we must have formed the decision to make it. And
this decision is an internal voluntary process. Internal voluntary
actions, then, are possible without external ; but external acts
always require antecedent internal ones.

§ HI

External voluntary actions, therefore, presuppose as their con-
dition internal volitional processes. And in like manner reflec-
tion and choice between various possible actions (which are
usually and wrongly held to be the essence of will) imply the
pre-existence of simple voluntary actions. In these latter some
definite object, whether it be something external or an internal
idea, is willed, without any reflection or choice at all. Choice is
nothing but a complex voluntary process. At first several
motives to will are present simultaneously. Later some one of
these, which accords with the decision we have formed, gains the

Simple and Complex Voluntary Acts 229

predominance over the others. If this predominance is exclu-
sive enough to allow one definitely directed volition to prevail
over the others, but not strong enough to give rise to an external
voluntary action, we have simply a desire. If the inhibitions
due to conflicting voluntary impulses are gradually overcome,
desire subsequently passes over into a voluntary action. This
explains the fact that desire may exist in two forms, — first as
the state of mind preliminary to a voluntary action, and secondly
as a permanent conscious process which does not give rise to
any such action. If in the latter case there is connected with
the desire the idea that it cannot be realised either for the
present or at all, we have what is called a wish. Desire, then, is
mainly a matter of affection and conation, while in wish there is
present besides these an intellectual process of considerable
intensity. But the popular view that desire is the uniform and
necessary antecedent of volition is the result of the erroneous
doctrine of will which we have just been discussing, and is entirely
without foundation. It follows from the conditions which we
have enumerated that desire may be present in the mind before
a voluntary act occurs, but it is not indispensable ; indeed, it is
probably absent oftener than it is present. Even in complex
voluntary processes the action may take place before the state
of desire has had time to develop. And in simple processes
the possibility of desire is altogether excluded, since the internal
voluntary action gives rise directly to the external without find-
ing in consciousness any resistance to be overcome. Feelings,
of course, occupy an entirely different position. They are
always present alike in simple and complex conative processes,
the only difference being that they are more complicated in the
latter case than in the former. Before volition is realised in
action, the tendency of will is known, and this tendency is
simply a matter of feeling. Feeling, therefore, is not a process
different from volition, but simply a constituent of the complete
voluntary process. It is only because we have so often had
experience of feelings from which no voluntary acts arise that
we are able to separate the two processes. The reverse is
altogether impossible : voluntary activity always presupposes
an antecedent voluntary tendency, i.e., a feeling.

What is it that must be added to feeling in order that a

230 Lectures on Human and Animal Psychology

volition may result ? This question has really been answered in
what has just been said. The tendency to will contained in the
feeling passes into a voluntary activity of the same direction.
What exactly are we to understand by this activity, which,
together with feeling,constitutes the chief characteristic of volition ?
The concept of activity contains two factors, — in tht first place,
activity implies a process or change in the given condition of an
object, and, secondly, the reference of this change to some
subject as its immediate cause. Thus in the physical sciences we
speak of the chemical action of the electric current, of the
mechanical action of wind and water, etc. The chemical
decomposition of a liquid into its constituents, the movement of a
mill-wheel, etc., are in these instances the observed changes ; the
electric current, the moving water, and air are the subjects to
which these changes are referred. So that we may ask in this
matter of voluntary activity, what is the change that occurs, and
what is the subject which we postulate to explain it ? In the first
place, the change is always an alteration in our states of
consciousness : an idea may arise which was not previously
present, or an existing one may disappear ; or, again, the change
may consist in an obscure idea becoming clearer, or a clearer one
more obscure, etc. These ideational processes are further always
connected in consciousness with various feelings and emotions.
In external voluntary actions the changes which refer to move-
ments of the body play the most important part. If we
abstract from the active subject, it is muscle-sensations, and
perceptions of movements and their results, which form the
chief conscious constituents of an external voluntary action ; and
all or some of them have now and again been regarded as the
exclusive characteristics of volition. But it is surely evident
that they do not exhaust the psychological analysis of will ;
every one of the changes in ideational content to which volition
may give rise can under certain circumstances occur inde-
pendently of it. Ideas which are brought to consciousness by
voluntary recollection may also crop up through involuntary
association ; and muscle-sensations may be produced by re-
flexes, or, as you know, by means of external and artificial
stimulation of the muscles. What must be added to all this,
therefore, is the reference to an active subject, which introspec-

Simple and Complex Voluntary Acts 231

tion teaches us to regard as the direct cause of the ideational
changes. But what is this ' active subject '? The most obvious
answer appears to be : the willing subject is our own self. But
that answer does not in any way assist our psychological analysis.
For what, again, is this 'self which we are led to look upon as
the author of our voluntary actions ? When we examine it
closely, we see that it is only another expression for the old
phrase 'willing subject.' We perceive changes in our conscious
content, and refer them to a single subject ; then we go on to
name these changes ' voluntary actions,' and the subject brought
in to explain them our ' self.' The only means of determining
more exactly the nature of the 'self is to analyse out what we
regard as the cause of our voluntary action in each particular
case.

Now the willing self is usually regarded as the immediate
cause of voluntary actions, but by no means as their final and
only condition. We suppose that the will is determined by
motives. We assume, of course, that a motive cannot be
effective without a willing self ; but, on the other hand, we regard
it as equally obvious from the facts of our immediate internal
experience that a willing self cannot act without motives. The
connection between motive and will is, therefore, just as
necessary as that between will and active subject. A reflex, or
a passive movement which some external force compels us to
make, is not conditioned by motives, although they have causes
of their own just as certainly as voluntary actions. Motives are
therefore causes of volition \ and since volition always arises from
internal processes, it is at once clear that they must be internal,
psychical causes.

Now what is a motive ? It is customary to make a distinction
between simple and complex motives, and to comprehend under
the latter rubric complex groupings of motives, where the con-
stituents may to some extent operate in different directions.
But in giving an account of the particular causes which deter-
mine volition, we shall only recognise as determinate motives
those which give it a definite direction, and which act like simple
forces, incapable of further analysis. In this sense every motive
is a particular idea with an affective tone attaching to it. And
since feeling is itself simply a definite voluntary tendency, this

232 Lectures on Human and Animal Psychology

combination of idea and feeling in motives only means that an
idea becomes a motive as soon as it solicits the will. Hence it
is tautological to say that only ideas with a strong affective tone
can operate as motives, since it is just the affective tone of an
idea which gives it the power of acting as a motive.

Nevertheless, introspection can show the conditions in virtue of
which some ideas become motives and others do not. These
conditions are of two kinds, — they consist partly in the imme-
diate attributes of sense-impressions, partly in the nature of our
previous conscious experiences. All those attributes of sensation
which endow it with a vivid affective tone serve also to make
the impression effective as a motive to will. In this case it
generally happens that the impression, with its strong affective
tone, is the only motive present in consciousness : the voluntary
action is a simple, or, as it is ordinarily expressed, an impulsive,
action. There can be no doubt that the majority of the actions
of animals are of this character. But impulses make up a large
part of human action also, and especially in the earlier stages of
its development. All sense-impulses are simply tendencies to
will connected with definite sensations ; i.e., they are feelings
which have a strong tendency to pass over into actual volition.

But in course of time the mind acquires various dispositions
toward the renewal of previous ideas which are themselves
connected with definite voluntary tendencies. An external
stimulus will not any longer simply call out the impulse corre-
sponding to it ; but this impulse will increasingly tend to influence
and be influenced by the dispositions already existing in the
mind. These, again, may be transformed into conscious motives
to will either by the external impression or by secondary
influences. So that the chief motive of actual volition is hence-
forth not some particular sense-impression which happens to be
there, but the entire trend of consciousness as determined by
its previous experiences. This trend or disposition does not, of
course, come directly to consciousness as such. We can only
give an account of those dispositions which enter into the con-
flict of motives in virtue of their perception as ideas to which a
strong affective tone attaches. And even of these many remain
so indistinct, that though they may be factors in the resultant
total feeling, and therefore in the act of will which finally results,

Psychological Elements in Voluntary Action 233

there is still no clear perception on our own part of their indepen-
dent existence. On the other hand, we can know nothing what-
ever of the influence which may be exerted by the dispositions
that never become realised in idea at all upon the changes in
our ideational content, and so upon the final act of will. The
links which join the actual current processes with the past
history of consciousness simply serve to bring out with unmis-
takable clearness the general fact that the determining ground
of action has not been any single impression, nor any particular
motive, whether called up by association or arising ' of itself/
but the entire trend or tendency of the mind, which has its roots
in the original nature of consciousness and the accumulated
experience of the mental life. A more or less intensive feeling
is connected with this general idea, and becomes an essential
element in the common feeling of the moment. The action which
results from this plurality of conflicting motives we call a complex
voluntary action or a volitional action. It possesses two distin-
guishing marks in consciousness1, — first, the feeling of a decision,
preceding the action and based upon the connection of the
present impression with past experiences ; and secondly, the
idea of the voluntary act as determined by a choice between differ-
ent and conflicting motives. Either one of these characteristics
may be more or less distinct. The clearness of the perception of
either usually stands in inverse ratio to that of the other. The
feeling of decision is predominant where the voluntary act
occurs at once and with complete certainty ; the feeling of
choice prevails where there is a long preliminary conflict of
motives.

These facts make it obvious that simple voluntary actions are
the necessary presuppositions of the more complex. Even in
the former the impression does not cause the action of itself ;
its effect depends upon the state of consciousness at the time.
But as this effect is relatively simple, the directly given stimulus
is the principal motive in the decision, and other motives have
no appreciable significance as compared with it.

§ IV

If we bring together once more all the essential elements of
a voluntary action, we see that it consists, in the first place, of a

234 Lectures on H^tman and Animal Psychology

/ feeling, in which the tendency of the will is manifested; secondly,
in a change in ideational content, which may be accompanied by
an external effect mediated by the organs of movement ; and
thirdly, in the general idea of the dependence of this change upon
the whole trend of consciousness. This last, like all secondary
ideas, finds its principal expression in a feeling, which partly
precedes the decision of will (in the form of the above-mentioned
feeling indicating the volitional tendency), and partly accom-
panies it. To these three constituents must be further added
the feelings which arise subsequently as a result of the internal
and external effects of the action, but which exert no influ-
ence upon its performance.

One very important attribute of volition, which affects all the
elements of voluntary action which we have here cited, is its
unity. Despite the conflict of motives and the oscillations of
feeling conditioned by it, the voluntary act itself at any given
moment must be single and unitary. This fact is the basis of
the unity of the self. By a hysteron proteron which often recurs
in psychology we tend to regard the latter as the cause of the
unity of volition. But, as a matter of fact, what we call our
' self is simply this unity of volition plus the univocal control
of our mental life which it renders possible. Furthermore, this
unity of volition enables us to explain directly another fact to
which we have already referred, — the fact that the feelings of
each moment unite in a single total feeling, whatever oppositions
may exist between them. This total feeling is the resultant
volitional tendency. And it is just as impossible for it to be
resolved into a number of independently coexisting feelings as
it would be for us to will several different things simultaneously.

In virtue of the attributes reviewed in these lectures, feeling
and will react upon the ideational side of our mental life ; and
thus help to determine the entire content of what we call, by an
arbitrary distinction, but one which is of service in the analysis
of the facts, consciousness. Now that we have described the
various constituents which go to make up the mental life, we
will turn for a time to the phenomena which result from the
combination of all of them.

LECTURE XVI

I. THE CONCEPT OF CONSCIOUSNESS. § II. CONDITION OF IDEAS IN
CONSCIOUSNESS. § III. PERCEPTION AND APPERCEPTION ; CLEAR-
NESS. AND DISTINCTNESS OF IDEAS. § IV. PHENOMENA ACCOMPANY-
ING APPERCEPTION. § V. ATTENTION. § VI. SELF-CONSCIOUSNESS,

§ I

WHAT is 'consciousness'? Much attention has been
devoted to this question in modern times both by
philosophers and psychologists. There could be no doubt that
the word denoted some phase or aspect of our mental life, and
was not identical with any of the other concepts, like ' idea/
' feeling,' ' will,' etc., which we apply to particular mental pro-
cesses and states. So that the view naturally suggested itself
that consciousness is a special mental condition, requiring to be
defined by certain characteristic marks. And the feeling that it
was necessary to oppose to consciousness an unconscious mental
existence promoted this opinion. Ideas^ affective processes,
may vanish and then again appear. It is therefore inferred
that after leaving consciousness they have continued to exist
in an unconscious state, and at times return to their former
condition.

From this point of view, nothing is more natural than to
think of consciousness as a kind of stage upon which our ideas
are the actors, appearing, withdrawing behind the scenes, and
coming on again when their cue is given. And the notion has
become so popular that many philosophers and psychologists con-
sider it much more interesting to learn what takes place behind
the scenes, in unconsciousness, than what occurs in consciousness.
Every-day experience, it is supposed, has made the latter familiar
to us ; but we know nothing of the unconscious, and to learn
something about it would be a really interesting addition to our
knowledge.

236 Lectures on Human and Animal Psychology

Nevertheless this comparison of consciousness to a stage is
entirely misleading. The stage remains when the actors have
left it ; it has an existence of its own, which is not dependent
upon them. But consciousness does not continue to exist when
the processes of which we are conscious have passed away ; it
changes constantly with their changes, and is not anything
which can be distinguished from them. When the actor has
left the stage, we know that he is somewhere else. But when
an idea has disappeared from consciousness we know nothing
at all about it. Strictly speaking, it is not correct to say that
it subsequently returns. For the same idea never returns. A
subsequent idea may be more or less similar to an earlier one ;
but it is probably never exactly the same. Sometimes it has
constituents which the earlier idea had not ; sometimes certain
of those which belonged to the latter are lacking in it. There
is scarcely any view which has been a greater source of error in
psychology than that which regards ideas as imperishable objects
which may appear and disappear, press and jostle each other,
objects to which, it is true, additions are at times made through
tne action of the senses, but which, when once they have come
into being, are only distinguished by the variation in their
distribution in consciousness and unconsciousness, or at most,
by the different degrees of clearness which they possess in con-
sciousness. As a matter of fact, ideas, like all other mental
experiences, are not objects, but processes, occurrences. The idea
which we refer back to a previous one, when we apprehend it
as similar to that, is no more the earlier idea itself than the word
which we write or the picture which we draw is identical with
the same word which we wrote previously or the similar draw-
ing which we made sometime ago. Indeed, you will see, if you
consider the complex conditions under which our inner experi-
enc*. arises, that nothing like the same degree of similarity
between the earlier and the later product can be expected here as
may be found under certain circumstances in the field of external
actions like writing and drawing. The circumstance that new
processes exhibit relations and similarity to others previously
existing, can no more prove the continued existence of the idea
as such, than it can be inferred from the similarity of the move-
ment of the pen in writing a definite word now to that involved

The Concept of Consciousness 237

on a former occasion, that this movement has continued to exist
in an invisible form from the time it was first made, and has
simply become visible again when we have written the word
anew. If ideas are not imperishable facts, but transitory pro-
cesses which recur in more or less altered form, the whole of this
hypothetical structure falls to the ground. And at the same
time the unconscious loses the significance ascribed to it as an
especial kind of mental existence, which, though not itself con-
sciousness, might at any rate enable us to determine the character-
istics or conditions which must attach to the objects of mind in
order that they may become conscious.

In the same way, all attempts to define consciousness as a
particular mental fact co-ordinate with our other internal experi-
ences have proved fruitless. It is obvious that those who would
regard it as the capacity of internal observation,* as a kind of
'internal sense/ commit in this analogy an error similar to that
involved in its comparison to a stage. The perceiving organ
and the perceived object are two different things ; consciousness
and conscious process are not. The activity of observation, of
attention, is of course found among what we call conscious pro-
cesses. But it is just one conscious fact, co-ordinate with the
rest, a fact which presupposes the existence of consciousness,
not one which renders consciousness possible. The same criti-
cism applies to yet another explanation which is sometimes
given. We distinguish in consciousness, it is said, a whole
number of ideas. Therefore consciousness must possess the capa-
city of discrimination ; the word must be equivalent to discrimi-
nating activity. But here again the question arises whether th«
discrimination of processes directly perceived is the antecedent
condition of these processes, or whether it is not rather a result
to which they are essential. In the first place, the objects must
be there to be distinguished. The child runs together a number
of separate objects into a single idea, where the developed
consciousness keeps them separate. Discrimination, then, like
observation, consists in processes which presuppose conscious-
ness, and which consequently cannot constitute its essence.
And consciousness itself is not a particular mental process, co-
ordinate with others ; it consists entirely in the fact that we
have internal experiences, that we perceive in ourselves ideas,

238 Lectures on Hitman and Animal Psychology

feelings, and voluntary impulses. We are conscious of all these
processes in having them ; we are not conscious of them when
we do not have them. Such expressions as ' the limen of con-
sciousness/ ' appearance in and disappearance from conscious-
ness,' etc., are pictorial ways of speaking, useful for the brief
characterisation of certain facts of internal experience, but
never to be regarded as a description of these facts. What
really takes place in the raising of an idea above the limen of
consciousness is, that something occurs which had not occurred
previously. And what really happens when an idea disappears
from it is that some process ceases which has hitherto been in
progress. In like manner we must think of the range of con-
sciousness as denoting simply the sum of mental processes
existing at a given moment.

Although, therefore, consciousness is not an especial kind of
reality co-ordinate with the particular facts of consciousness,
modern psychology still finds the concept indispensable. We
must have a collective expression for the whole number of
mental experiences, given either simultaneously or successively.
As simply denoting the existence of internal experiences, while
leaving their nature altogether undetermined, the concept is
especially serviceable for the treatment of the interconnection
of the mental facts, of all those processes with which we have
already become acquainted in isolation. It has no meaning
apart from its reference to this interconnection of simultaneous
and successive mental processes ; and the problem of conscious-
ness consists in determining how the particular phenomena are
interrelated, and how their relations and connections again
combine to form the totality of mental life. For the sake of
simplicity in treatment, it will be convenient to confine ourselves
at first to the ideational side of consciousness, and then, when
we have discussed the problem just formulated from this point
of view, to supplement our results by reference to the affective
and conative elements. This is of course the plan which we
have followed in our analysis of particular mental processes. It
will, however, soon become evident that in dealing with the
interconnections of mental processes we cannot carry our
abstraction through to the end, since the affective side of our
mental life constantly exercises a determining influence upon

Condition of Ideas in Consciousness 239

the combinations and relations of ideas. In certain instances,
therefore, we shall not be able to avoid at least a passing refer-
ence to the affective and conative factors.

The first question which may be raised within the limits of
the conditions laid down runs of course as follows : how many
ideas may be present in consciousness at a given moment ? The
content of this question is not quite so precise as its wording
seems to imply. The estimation of the number of constituents
which a whole contains is, naturally, dependent upon what we
regard as the constituent unit. Now, even if we neglect the
continual change among ideas, their combinations in conscious-
ness are enormously complex. So that it may easily be a matter
of doubt whether some given portion of conscious content is to
be considered as an independent idea, or as a part of a more
comprehensive idea. We may here dispense for a time with
any final theoretical solution of this difficult preliminary problem.
For our present purpose it will suffice if we can furnish a practical
criterion. We shall accordingly regard an idea as separate and
independent when it is not connected by customary association
with other ideas simultaneously present. If, e.g., there is placed
before the eye a number of letters in serial order (say, x v r t},
we shall consider that each one forms an independent idea by
itself, in spite of its spatial association with the rest For, re-
garded as a whole, letters form no new complex idea, capable
of entering into definite connections with other ideas. If, on the
other hand, we perceive four such letters as w o r k, we shall
not hold them to be independent ideas, — at least, for one who
reads them as a word, — but shall look on them as combined into
a single complex idea. From these considerations there follow
two results, which should never be lost sight of in experiments
made to determine the ideational range of consciousness. First,
we must always decide from the objective and subjective con-
ditions operative in each particular instance what ideas may
pass as independent units and what not. It is, of course,
obvious that the same objective impression may in one case be
apprehended as one idea, and in another as more than one,aocord-

240 Lectures on Human and Animal Psychology

ing to the subjective conditions involved. Secondly, the con-
clusions derived from ideas of one kind will not necessarily hold
for ideas of any other kind. In particular we may expect to
find that the range of consciousness will be smaller for complex
i'deas than for relatively simple ones.

When the question of the range of consciousness was first
raised, these conditions were entirely overlooked, and the general
•nethod of investigation pursued was not one which could lead
*,o any certain results. Conclusions were either deduced from
:ertain metaphysical postulates, — e.g., that the mind, as a simple
Deing, could only contain a single idea at a given moment, — or
:he investigations were based solely on introspection. Any
Dne may convince himself of the fruitlessness of this latter pro-
cedure by seriously asking himself the question : how many
ideas do I now find in consciousness ? And at the same time
the experiment shows him the reason why his efforts at an
answer are withoui result. The question is scarcely raised be-
fore the moment to which it refers has passed, nor can the
following moment be fixed any more successfully. It thus be-
comes quite impossible to distinguish what is simultaneously
given at a particular moment from that which comes later.
This defect of direct introspection, however, itself shows us how
we should endeavour to supplement it by experiment. It is
only necessary so to arrange the conditions of experimentation
that the confusion of simultaneous impressions with successive
is less easily possible. This we can do by momentarily present-
ing a number of sense-impressions, which are capable of becom-
ing independent ideas, at a given signal, and then trying to
determine how many of them have been actually ideated. Now
it would be wrong to suppose that the running together of the
momentary impression with subsequent ideas is here altogethei
precluded. Suppose, e.g., that by a momentary illumination we
present to the eye a number of visual objects. The perceptions
of the first moment will naturally be supplemented by others of
which we do not become conscious until later. You may easily
convince yourselves of this by holding a book in the dark at a
convenient distance from the eye and illuminating the room
for an instant by an electric spark. Even if in the first moment
you only cognised a single word, it may very well happen that

Condition of Ideas in Consciousness 241

you will subsequently, by the aid of memory, be able clearly to
apprehend others. Indeed, what is read subsequently in this
way is often more than what was recognised in the first instance.
But these experiments, again, lead us to a furrtier fact, which
shows that it is possible to draw valid inferences from them
with regard to the condition of consciousness at a given moment.
We can very clearly distinguish the image that has been gradually
reconstructed on the basis of the original impression from the
image which corresponds directly to it. This is due to the fact
that the particular moment is not precisely like those which
directly preceded or follow it : the sudden appearance and dis-
appearance of the flash of light marks it off from them ; this
distinction makes it less difficult for introspection to neglect or
voluntarily to exclude the subsequent filling out of the original
ideational image. Here, as everywhere, psychological experi-
ment does not enable us to dispense with introspection, but, on the
contrary, renders introspection possible by furnishing the condi-
tions which it requires for exact observation.

Experiments of this kind with momentary impressions may be
made in any sense-department. But visual impressions are best
suited to the purpose, because they can most easily be selected
with a view to their apprehension as independent ideas. The
impression itself is, it is true, not entirely momentary ; light-
stimulation has a physiological after-effect. However, in
impressions which pass very quickly this after-effect is so short
that we may neglect it for our present purpose. Visual experi-
ments are .made with the apparatus represented in Fig. 37. It
is intended for the demonstration of the phenomena to a large
audience. If you should merely wish to perform the experiment
upon yourselves, the dimensions could, of course, be very much
smaller. The apparatus consists of a black screen, held in
grooves in front of a black vertical board, some two metres high,
and falling when the spring F is pressed. In the screen there is
a square opening large enough to enclose a large number of
objects that can be separately ideated, such as letters of the
alphabet. This opening is so placed that when the screen is
raised it shows simply the dark background, but during its fall
passes very quickly before the objects to be observed, and
instantly covers them again. On the part of the screen below

242 Lectures on Hitman and Animal Psychology

the square opening a small white circle is so placed that before
the fall of the screen it exactly covers the centre of the visual
surface afterwards briefly exposed to view. This circle serves as
a fixation-point to put the eye in the most favourable position
for the apprehension of the impressions. A in the figure gives a

lateral, and B a front,
view of the apparatus.
In A the screen is
raised, and covers the
objects which are to be
seen ; in B it is repre-
sented in the moment
of falling before them,
so that a number of
impressions ( letters
taken at random) have
just become visible.
If we imagine the
motion continued, we
shall have these hidden
again the next moment
by the upper, closed
part of the screen. The
size and distribution of
the visual objects and
the distance of the
observer from the
apparatus must be so
chosen that all the
separate letters which
are to be seen shall
fall within the region
of clearest vision. It
3 is of course' true that

*IG> 37> in these experiments

every visual object is, strictly speaking, visible not only for a
single moment, but for a measurable, although relatively small
portion of time ; and, further, that this time is not exactly the
same for the different objects. In the apparatus represented in

Condition of Ideas in Consciousness 243

Fig. 37, the upper line is visible for O'OQ", the lower for O'O/",
and the middle for O'O8". These times are, however, so small in
comparison with the much greater duration of the after-image
that for our present purpose they may be regarded as really
momentary.

Experiments of this kind show that four, and sometimes even
five, disconnected impressions (letters, numerals, or lines of
different direction) may be distinctly perceived. If the separate
impressions are so arranged that they enter into combination
with one another in idea, the number becomes three times as
great. Thus we are able to cognise instantly two dissyllabic
words of six letters each.

But the result of such investigations is to call our attention to
other phenomena, which render it obvious that we cannot really
learn anything in this way regarding the total range of conscious-
ness. We notice that the letters, numerals, words, etc., which we
clearly apprehend at the moment when the screen falls, by no
means exhaust the conscious content of the moment. Besides
these impressions which are clearly apprehended, there are
present in consciousness others which are less distinct, or wholly
indistinct. In addition to the four or five letters which you were
able to read, you would have noticed, e.g., some of which you
cognised only the approximate outline, and others about which
you had only the quite indefinite idea that they were present and
were visual impressions. The experiments show, therefore, that
this method can only enable us to determine the number of clear
and distinct ideas present in consciousness, and can give us no
information of the entire number which it contains. The number
of clear ideas for the sense of sight amounts to 4 or 5 when
they are comparatively simple and familiar ; if they are complex,
the number varies from I to 3, according to the degree of
complexity. In the latter case the number of simple ideas
present in a clear ideational complex may be as many as 12.
You will notice, further, that the impression falling directly upon
the yellow spot is usually more distinctly apprehended than any
of the others. But this is by no means necessarily the case ;
laterally seen objects may take precedence over the objects
seen directly, especially if the attention is voluntarily directed
upon them.

244 Lectures on Human and Animal Psychology

§ HI

So that, even although our first method has told us nothing of
the actual range of consciousness, it is worth while to spend a
little time in examining the results obtained. Apart from the
information they afford us as to the number of ideas clearly
apprehensible at a single moment, their indication of different
degrees of ideational clearness is particularly worthy of remark.
It is true that the distinction of clear and obscure ideas did not
escape the keen observation of Leibniz, and since his time has
scarcely been disputed. But ordinary introspection does not
admit of such definite and direct determination of the relations
of the different degrees of clearness as that afforded by the
method of instantaneous impressions. The experimental method
demonstrates, e.g., the correctness of Leibniz' hypothesis that
there is no abrupt transition, but always a continuous gradation
from each degree of ideational clearness to the next. In the
experiment with momentary visual impressions given above, we
distinguished tJiree kinds of ideas in consciousness : the clear,
the more obscure, — where a partial discrimination is still possible,
— and the quite obscure, in which we only cognise the presence
of some conscious content belonging to a definite sense-depart-
ment We must now understand that these ideas only differ in
degree of clearness, and that all three degrees are connected by
continuous gradations. For the two extremes, however, we may
employ the terms which Leibniz introduced. We may term the
appearance of an obscure idea in consciousness a perception, and
the appearance of a clear one an apperception. These two names
must not be understood to carry with them any presuppositions,
either metaphysical or psychological. They merely express a
fact, for which (as is usual in science) we choose the name pro-
posed by the investigator who first called attention to it. We
leave out of account any assumption, any theory, derived from the
observed facts which Leibniz and his successors may have con-
nected with these terms. Notice only that the relation of clear
to obscure ideas furnishes an obvious analogy to that of objects
distinctly or indistinctly seen in the field of vision ; and that it
is therefore natural to refer the distinction of perception and
apperception to consciousness itself, just as in external vision we

Clearness and Distinctness of Ideas 245

account for the different degrees of distinctness by reference to
differences in acuteness of vision in different portions of the
visual field. We may say, then, that the perceived ideas are those
which lie in the field of consciousness, while the apperceived are
situated at its fixation-point.

Now what are we to understand by the clearness of an idea ?
The word, like all the names of psychological concepts, has been
transferred from external objects to the conscious subject. We
use the term ' clear ' to denote luminous or transparent objects ;
i.e., those which are themselves easily perceived, or which aid the
sense of sight in perceiving others. When the word is applied
to consciousness, therefore, it must express some similar cha-
racteristic in introspection. An idea is clear when it is appre-
hended in introspection more perfectly than others which, in
contradistinction to it, are called obscure. The only difference
between the original and the transferred meaning of the words
is this : in the former case the property of clearness may belong
to the object without reference to our perception of it, but in
the latter the idea is only clear in so far as it is clearly perceived
in consciousness ; a difference which again has its source in the
fact that our perceptions of mental processes and the mental
processes themselves are completely identical. Ideas are only
ideas in virtue of our perception of them. Internal perception
(introspection) is simply the fact of internal experience itself ;
and we are only looking at this experience from different points
of view when we speak of it at one time as idea, feeling, etc.,
and at another sum it up as internal perception.

We are apt to identify the clearness of ideas with their
distinctness, and to define one of these concepts by the other,
' distinct ' being ' what can be clearly cognised,' or ' clear '
* what we perceive distinctly.' Now it must be admitted that
the two properties are generally found together. But they are
not at all identical ; each of them denotes a different aspect of,
or a different reason for, the advantage which a given idea
possesses in consciousness. An idea is ' clear ' solely in virtue
of its own properties, just as in the use of the word in external
reference pure water is termed ' clear,' and not ' distinct,' because
it is transparent, so that any object that happens to be in it may
be seen through it. On the other hand, an idea is called

246 Lectures on Human and Animal Psychology

' distinct ' with reference to the definiteness with which it is
marked off from other ideas. Thus an object lying in clear
water is distinctly seen because it stands out sharply from its
surroundings. Similarly a tone is clear when we can fully
apprehend its peculiar quality ; it is distinct when definitely
distinguishable from the other elements of a compound clang, or
from other simultaneous sound-impressions.

As applied to our ideas, then, clearness and distinctness
denote properties which depend directly upon the activity of
ideation, or, what is the same thing, of introspection. One and
the same idea under the same objective conditions may be at
one time clear, and at another more or less obscure. And for
this reason we must be especially careful not to confuse the
clearness of an idea with its intensity. That is simply dependent
upon the intensity of the sensations which constitute it. The
intensity of perceptual ideas is determined by the strength of
the sense-stimuli, that of memorial ideas by other conditions,
which have nothing to do with ideational clearness. At the
same time intensity usually promotes clearness and distinctness.
Other things equal, the more intensive idea is usually the clearer,
and very weak ideas in particular are but seldom clear and
distinct. Nevertheless it may happen, if the subjective condi-
tions of perception so determine, that an intensive idea is obscure
and indistinct, and a weak one clear and distinct. A very weak
over-tone in a clang, e.g., may be heard clearly and distinctly,
while the more intensive ground-tone is less clearly perceived,
and a loud noise simultaneously given perhaps hardly noticed at
all.

It follows from all this that the clearness of ideas necessarily
depends upon the condition of consciousness for the time being.
Inasmuch as they help to determine this condition, the intensity
of impressions and memorial images also exerts an influence upon
the clearness and distinctness of ideas. But since the state of
consciousness is certainly not entirely dependent upon those
conditions, they are by no means the only factors of importance
in the matter. Our final definition of clearness must, therefore,
be that it is that property in -virtue of -which an idea has an
advantage over other ideas in introspection. But it is not difficult
to see that this definition is only a description of the word

Phenomena accompanying Apperception 247

' clear.' As a matter of fact, it is just as impossible to define the
clearness of an idea as to define the intensity or quality of a
sensation. We can distinguish these fundamental properties of
our mental processes from each other by showing that under
definite conditions they vary separately and independently.
But the differences could no more be brought home to one who
had not experienced them than can the distinctions of colour to
the congenitally blind.

§ IV

On the other hand, the becoming clear of an idea is regularly
associated with other mental phenomena, which not only assist
the introspective discrimination of clear and obscure ideas, but
also throw some light upon the subjective conditions of the
processes which we have distinguished as perception and apper-
ception. These phenomena are of two kinds, — they consist
partly of sensations, partly of feelings. The sensations which
jtccompany apperception belong to the category of muscle-sen-
.ations. They are especially noticeable in cases of external
.sense-perception. If we are directing our attention upon a
particular tone, or a particular visual object, to the exclusion
of other impressions of light and sound, we have in ear or
eye definitely graduated muscle-sensations, which are probably
referable to the tensor tympani and to the muscles subserving
the accommodation and movement of the eye. The same sen-
sations may be perceived, though less clearly, to accompany
memorial ideation, at least when the ideas are vivfd. An
object seen with the mind's eye is referred to a certain distance
from us, and we consequently accommodate the muscular
apparatus of our eye to it. The tones of a melody which we
recall in memory may give rise to a tension in the ear as clearly
perceptible as though they were real. Even the fainter pictorial
ideas which constitute abstract thinking are not wholly without
this sense-accompaniment. When we are trying to remember
a name or are pondering a difficult problem we notice the
presence of strain-sensations. These are partly sensed in the
eye, — visual ideas being, as you know, predominant in conscious-

248 Lectures on Human and Animal Psychology

ness, — partly in the forehead and temples, where the muscles
lying directly beneath the skin, which play a part in mimetic
movements, are strained to a degree more or less proportioned
to the amount of internal effort.

The connection of these muscular tensions with mimetic ex-
pressive movements leads us directly to the second accompani-
ment of the apperceptive process, — to feeling. There could be
no emotional expression without feeling. Feelings precede ap-
perception proper, and continue to exist during the course of the
process. They are different in the two cases, though their
passage in consciousness is continuous, so that those which
precede apperception and those which accompany it form an
affective totality, which by the fact of its continuity resembles
emotion (of which we have to speak later), and which indeed nol
infrequently becomes actually transformed into emotion. Out
perception of these attendant feelings, like our perception of the
sensations discussed above, is most distinct when the clearness
of their ideational substrates is very great, and especially when
this clearness is mainly the result of the trend of consciousness,
itself, and not of external conditions ; e.g., to put it again con-
cretely, when we are voluntarily recalling an idea which we
have previously had, or when we are expecting an impression,
etc. Even when the condition is not one of expectation proper,
the feeling preceding apperception is very closely related to that
of expectation. The feeling accompanying the process, on the
other hand, may be compared to that of satisfaction, to the re-
laxation of a tension, or, again, if the expectation is not realised,
to that of disappointment or failure. It is quite true that these
feelings are only clearly perceptible under the special conditions
which characterise expectancy, recollection, etc. But careful in-
trospection seems to show that feelings of the same kind are
never entirely absent where ideas which were formerly obscure
become clearer, even although their intensity be much less and
their quality exceedingly variable. At least, if there is any es-
sential difference, it is only in the case of the antecedent feelings.
Their period of duration, e.g., may be very much shortened
(though they hardly ever entirely disappear) when the object of
apperception is an external sense-impression, or vhen memorial
images crop up unexpectedly.

Attention 249

§ V

The whole circle of subjective processes connected with apper-
ception we call attention. Attention contains three essential
constituents : an increased clearness of ideas ; muscle-sensations,
which generally belong to the same modality as the ideas ; and
feelings, which accompany and precede the ideational change.
At the same time the concept of attention proper has no
reference to the first of these processes, but only to the last two.
Apperception, therefore, denotes the objective change set up in
ideational Content, attention the subjective sensations and feel-
ings which accompany this change or prepare the way for it.
Both processes belong together, as parts of a single psychical
event. It may happen in certain instances that the objective
effect is distinct, while the subjective aspect of the process does
not attain a liminal intensity. Or it may happen, as when an
expectation is unfulfilled, that the subjective constituent attains
a great intensity, while the objective is entirely overshadowed.
But these are only extreme cases of a series which, like all mental
series, contains terms arranged without break or interruption.
Attention in the wider sense is not, — and this is the important
point, — a special activity, existing alongside of its three consti-
tuent factors, something not to be sensed or felt, but itself
productive of sensations and feelings. No! in terms of our own
psychological analysis at least, it is simply the name of the com-
plex process which includes those three constituents. Their
nature makes it plain enough why we regard attention as subjec-
tive activity, without our needing to assume any special conscious-
ness of activity independent of the other mental elements. The
concept of activity always presupposes two things, — first, a change
in the condition of something ; and secondly, a subject whose
states vary with that change in such a way that the two can be
exactly correlated. We then regard the subject as the active
subject, and the changes set up as the effects of its activity.
Now the sensations and feelings constituting attention are not
accidentally and equivocally associated with the apperceived
idea, but stand in very definite relation to it. The attendant
strain-sensations and the preceding or accompanying feelings are
entirely governed by the nature of the apperceived idea ; if it

250 Lectures on Human and Animal Psychology

changes, they change also. So that the phenomena which go to
make up the apperceptive process possess all the characteristics
required by the notion of an activity proceeding from an acting
subject. This acting subject is given us simply and solely in the
sensations and feelings accompanying the act of apperception.
And since we find among these elements not only a constant
alteration, but also a continuous connection of earlier processes
with later, we come to regard the acting subject as persisting
through all its changes. Language has given an expression
to this view, which has been of determining influence upon the
further conceptual development of the distinctions in question, in
constantly rendering the notion of the permanent subject by
the sign for the first person in simple verb judgments.

§ VI

It is in this way that the concept of the self (' I ') arises : a
concept which, taken of itself, is completely contentless, but
which, as a matter of fact, never comes into the field of intro-
spection without the special determinations which give a content
to it. Psychologically regarded, therefore, the self is not an idea
among other ideas ; it is not even a secondary characteristic,
common to all or to the great majority of ideas ; it is simply and
solely the perception of the interconnection of internal experience
which accompanies that experience itself. Now we have already
seen that perceptions of this kind, — perceptions which refer to
the occurrence of a process, the manner in which it runs its course,
and so on, — are sometimes transposed back again into ideas.
There is a deep-rooted tendency to hypostatise mental events,
a tendency evinced by those theories which have regarded
ideas themselves as permanent objects (pp. ?2i, 222). And
there is a very special tendency to transpose the ' self into
an idea of this character, though, as a matter of fact, it is
nothing more than the way in which ideas and the other mental
processes are connected together. Since, further, the manner
of this connection at any particular moment is conditioned by
preceding mental events, we tend to include under the term
'self the whole circle of effects which have their causes in
former experiences. The 'self is regarded as a total force,

Self -consciousness 251

which determines particular events as they happen, unless, of
course, they are occasioned by the action of external impres-
sions or of those internal processes which we experience just as
passively as we do the external. And since the principal effect
of the preconditions of consciousness is the determination of the
appearance and degree of clearness of ideas, we further bring the
'self into the very closest connection with the process of ap-
perception. The self is the subject which we supply for the
apperceptive activity. It is plain enough that there is involved
here a transference of the relations observed in external percep-
tion to the sphere of internal experience. The self, you see, is
regarded after the analogy of external objects, which we take to
be the same in spite of variation in their properties, because the
variation is always continuous both in time and space. But
without the continuity of our mental life we should not be able
to cognise the continuity of objective things ; so that in this
interplay of developments we have the self figuring both as
cause and effect. The perception of the interconnection of
mental processes, which crystallises in the concept of the ' self,'
renders possible the distinction between objects and their chang-
ing properties ; and this distinction in its turn inclines us to
ascribe an objective value to the concept.

There is another reason for this in the fact that the body, with
which all the states of the self are connected, is itself an external
object. In the first place, the self is a product of two things, —
external perception and internal experience ; it is the body, to-
gether with the mental processes connected with it. Later on
reflection destroys this unity ; but even then there remains some
faint trace of that object-idea which attached to the self of sense.
And where the current view of life is the practical one, with its
naive sense-reference, the body takes its place unquestioned
as an inexpugnable constituent of the self.

LECTURE XVII

. DEVELOPMENT OF ATTENTION ; PASSIVE AND ACTIVE APPERCEP-
TION. § II. ATTENTION AND WILL ; FLUCTUATIONS OF ATTENTION.
§ III. RANGE OF CONSCIOUSNESS; FORMATION AND DIVISION OF
RHYTHMICAL SERIES.

SIMULTANEOUSLY with the development of self-con-
consciousness, which we described in the previous lecture,
proceeds the development of another complex process, — that of
attention. The two developments are in many respects similar.
States of attention, like those of self-consciousness, present
certain external differences which may be regarded as opposites ;
though it is true that, to place the opposition in a clear light,
we must more or less neglect intermediate processes which
would enable us to pass from one to the other. For the
extreme cases, however theoretically possible, never actually
occur in the purity in which they can be obtained by analysis.
However, if we disregard the concrete for a moment, we shall
find evidence enough for the general possibility of the extreme
cases.

We saw that in every act of apperception there are two
principal conditions of the resulting effect, — first, the momentary
condition of consciousness, itself determined partly by external
influences, partly by those of its own earlier states which are
directly related to these influences, and therefore with greater
or less regularity associated with them ; and secondly, the
entire previous history of consciousness, which may operate in
the most various ways to alter the effect due to this momentary
state. You must not, of course, suppose that these two con-
ditions are at work in the individual case in the sense of two
opposing forces. That would be impossible. For the earlier

Development of Attention 253

states which are directly connected with any particular
objective impressions, — ideas, feelings, or whatever these states
may be, — themselves form part of the previous mental history.
In other words, we have to do with a difference in degree, and
not with a difference in kind. But this does not prevent the
results in the two cases from appearing as opposites. Suppose
that the direction of the attention is determined merely by
some chance stimulus, and by a ' state of mind ' which is per-
manently associated with that stimulus, or has been brought
about by accidental circumstances. Then the immediate
impression which we have of our internal experience is that of
a passive receptivity of what is going on in our minds. Sup-
pose, on the other hand, that the direction of the attention is
determined by more remote conscious tendencies which have
arisen from previous experience, and which are not directly
related to the particular impressions of the moment. Then we
have always the impression of a productive activity. Apper-
ceptions of this kind we regard as actions of our ' self ; 'self is
just an expression for the total effect exerted by our previous
mental experiences as a whole, without particular reference to
any special components of those experiences, upon the mental
processes which are running their course at any given moment.
To make this difference clear, we will call the first form of
attention ' passive,' and the second ' active,' attention. Let me,
however, warn you again, even at the risk of repetition, that in
calling attention ' passive ' we by no means deny to it any
character of activity, that is, decline to see in it the operation of
previous experiences. The contrary is true : such experiences
are always operative ; it is only that the extent and direction
of their influence are limited and circumscribed. Neither is it,
of course, to be thought that external influences and the states
of mind that follow from them are wholly without effect in the
case of active attention. It is only true that they retire into
the background before the influences of dispositions established
during long periods of time and strengthened by mutual con-
nection ; they are none the less continually at work to modify
these dispositions. To repeat once more, we are dealing with
extreme cases, which can never occur in absolute purity, because
the processes on which they depend are the final terms of a

.254 JLectures on Human and Animal Psychology

continuous process-series. In both cases consciousness is
functioning in the same way ; the difference is only a difference
of more and less, of a greater and a narrower range.

If we could only appeal to the ideational side of mind, then,
we should not seldom find it difficult to decide in a particular
case whether a particular apperception were active or passive.
So that here again we find feeling playing a large part in our
immediate apprehension of our own actions. You remember
the general characteristic of feeling, — that its peculiar quality-
gives expression to the total attitude of consciousness. In the
present case, the presence of active apperception is invariably
and unmistakably indicated by a feeling of activity. We can
no more describe this than we can any other feeling ; we can
only attempt to determine it by enumerating those of its con-
ditions which belong to the ideational side of consciousness (cf.
Lecture XIV.). The degrees of intensity of this feeling give us
a direct measure of our own activity ; that is, of the preponde-
rance of our whole mental nature over momentary and transitory
excitations. There can be no doubt that we must regard it as
a total feeling in our previous sense of the word (p. 219). It
determines the attitude of consciousness at any moment. But
its own peculiar and variable quality is itself determined by the
special feelings dependent upon concurrent ideas and their
mutual connections. Even passive apperception, therefore, has
its attendant feelings ; only that these are associated to form
a total feeling with a character of its own, either exclusively
conditioned by the quality and intensity of the ideas that
happen to be present in consciousness, or (and this is especially
the case in apperception of very intensive external sense-
impressions) consisting in a feeling of inhibition, which appears
to arise from the sudden arrest of existing tendencies in the
formation of ideas. In its latter form it may be intensified by
sense-feelings of unpleasantness or pain, without, however,
being dependent upon these.

Considered from the point of view of these attendant feelings,
the process of apperception and attention appears in a con-
nection which points at once to those elementary mental
processes which we have already discussed. Feelings we found
to be invariable forerunners and concomitants of volition.

Development of Attention 255

They indicate the direction which an act of will will follow
before it has itself become conscious ; and when it has attained
its full force, they are still present to colour and explicate its
effect. A second characteristic of volition beside feeling is an
alteration in the state of consciousness on its ideational side,
referable not to external influences, but to past mental disposi-
tions. Both characters attach to the process of apperception,
and, since the conditions of each form of this process pass over
into one another without interruption, attach to active and
passive apperception alike. For the raising of an idea to a
higher level of distinctness can only come about in passive
apperception when there are present certain positive mental
dispositions to favour its preference. So that ideas and the
feelings that are connected with them serve as motives to the
act of apperception, while apperception itself shows all the
characteristics of an act of will. More than this, its two funda-
mental forms, the active and passive, obviously correspond to
the two fundamental forms of conative activity, — the passive
form, the impulsive act, and the active, or act of choice. We
act impulsively when we apprehend an impression under the
constraining influence of external stimuli, and of the ideas
immediately and directly aroused by them ; we choose when
out of a whole number of concurrent ideas we raise to a higher
level of distinctness some particular one which long-established
mental tendencies dispose us to regard as the fittest at the time.
And the coincidence of the internal with external voluntary
acts is proved by this, — that not seldom our decision is prefaced
by a clearly perceptible strife between different motives.

Now it is plain that these internal acts of will are not only
the analogues of the external, but at the same time their con-
dition. There can never be an external act save as the result
of a previous inner selection, and this holds again both of the
impulse and of the act of choice. So that apperception is the
one original act of will. It can exist without the consequences
which follow upon other acts of will, whereas these always pre-
suppose as their condition some internal act.

256 Juectures on Human and Animal Psychology

There is another property of apperception and attention that
demands consideration under the head of its relation to will,
and which plays an important part in the sequence of mental
processes. We observe an alternation in the internal activity
of attention, just as we find in external voluntary acts alternat-
ing periods of rest and activity, recurring either at regular
intervals, or, as the conditions chance to vary, after pauses of
varying length. You know, for instance, how difficult it is to
follow a lecture word for word with uniform attention. If it
were really necessary for our understanding of the whole that
we should apperceive each single word with equal clearness,
it would be altogether impossible to follow what is said. But
in most cases the context enables us to fill out passages to
which we have not been especially attentive. And, to a
certain extent, that holds also of the speaker. Language is
fortunately of such a nature that a whole number of verbal
ideas which are indispensable to the expression of thought
associate by frequent repetition to a scheme which comes, so
to speak, of itself; so that the attention may be rested while
the speaking is following the lines of the customary associa-
tion. We may assume that these fluctuations of attention
are, as a rule, pretty irregular : they vary with external im-
pressions and internal necessities. In other words, since its
two conditions change, we shall not expect to find in attention
as a whole any periodic function of consciousness. We are,
however, able, by special experimental arrangements, to intro-
duce regularity into the conditions, and to keep them practically
uniform for a considerable length of time. If this is done, we
still find that apperception is by no means constant at a certain
intensity ; it still rises and falls, and its periods, owing to the
uniformity of conditions, are fairly regular.

For the purposes of such experimentation it is best to employ
very weak sense-stimuli, such as can be easily perceived with
some strain of the attention, but fall below the limen of conscious-
ness with any relaxation. Under these conditions we find a
reciprocal relation to exist between intensity and distinctness of
ideas This is, of course, closely related to the law that intensity

Attention and Will ; Fluctuations of Attention 257

favours distinctness in ideation. If we allow a very weak impres-
sion which lies just above the limen of stimulus to affect a sense-
organ, any momentary relaxation of attention will allow it to
fall below the limen. In other words, the previously perceived
impression becomes imperceptible. This phenomenon may be
regarded in two ways. It may be considered, first, as a decrease
of sensation-intensity from the minimal perception-magnitude
to zero ; or it may be looked upon, secondly, as the sinking of s
previously relatively distinct idea below the limen of conscious-
ness. There is no real contradiction between the two interpre-
tations. The two sets of expressions can only be equivalents
if the concepts "stimulus-limen " and " limen of consciousness "
mean the same thing, regarded from different points of view :
an impression which passes the stimulus-limen crosses at the
same time the limen of consciousness. ' That is, the equivalence
of the two expressions is due to the fact that the stimulus-limen
is a value depending upon stimulus-intensity on the one hand
and upon the state of consciousness, — i.e., of attention, — on the
other.

Weak auditory stimuli furnish us with the simplest means
of observing the periodic fluctuations of attention under the
influence of constant conditions. If you place a watch, say at
night-time, when everything is quiet, at such a distance from
your ear that its ticking can be just heard with strained atten-
tion, you will find that at intervals of three to four seconds the
regularly recurring impressions alternately appear and disappear.
Very similar fluctuations of sensation maybe noticed if the skin
is stimulated by a uniform induction current of very slight
intensity ; only in this case the periods are somewhat shorter.
Sight can be best investigated, not by means of approximately
liminal stimuli, but by the aid of stimulus-
differences at the limit of noticeability.
The difference-limen, as we may call it,
takes the place of the stimulus-limen in the,
other two sense-departments; the differ-)
ence is alternately noticed and not noticed
The phenomenon may be very conveni-
ently studied on quickly rotating discs. A
small piece of a black sector measuring only FIG.

258 Lectures on Human and Animal Psychology

a few angular degrees is painted upon a white disc. In quick
rotation we have a grey ring on a white ground. If the sector
is made of the proper breadth, the ring will be just noticeably
different from its background. If you fixate it continuously,
you will find that it is alternately visible and invisible.

It has often been conjectured that the phenomena which we
have been describing are dependent upon purely physiological
conditions, lying in the peripheral nerves and organs of sense ;
e.g., upon a periodically restored exhaustion of the organs or
upon an alternation of strained and relaxed movement. But, so
far as the matter has admitted of experimental test, these hypo-
theses have not been confirmed. Where peripheral changes were
found, they proved to be either effects of the fluctuation of
attention, or secondary conditions which, though they might
affect the temporal course of the phenomena, were not the
occasion of them. It has also been noticed, especially in obser-
vations upon the concomitant feelings, that so soon as the
impression falls below the limen there is a sudden and stronger
strain of the attention, immediately attended by the reappear-
ance of the sensation. All these facts make for the assumption
that the phenomena in question belong directly to the sphere of
the functions of the attention. But we must not suppose, of
course, that these functions have no physical attendants, central
or peripheral. So that the conditions which serve to vary these
will also affect the time-relations of the fluctuations of attention.

§ HI

The instantaneous production of transitory sense-ideas, which
served in the first place to facilitate the investigation of the vary-
ing degree of ideational distinctness, has proved a method oi
widening our knowledge of a large number of important mental
phenomena. It has, however, been found inapplicable to the
problem of the range of consciousness for the solution of which
it was originally employed, just by reason of this continuous
gradation of the distinctness of ideas. At the same time,
observation of the effect of sudden visual impressions pointed out
the path which investigators of this problem must follow.

Suppose that, at a given moment, a complex impression affects

Range of Consciousness 259

the eye in such a way that only a part of it can be clearly
apperceived. It may be a large number of letters, or a compli-
cated geometrical figure (Fig. 37, p 242). And suppose that the
moment after, there is given either a similar or a somewhat
different impression. The comparison of the two complex
impressions is found to be based not only upon clear appercep-
tion, but also upon those constituents of the idea which had been
merely obscurely apperceived. It is not infrequently possible to
say in such a case that the two impressions are " alike " or
" unlike," without our having any account to give of the elements
which condition the judgment of unlikeness in the second
instance. It follows from this that the more obscure constitu-
ents of an impression are taken up into, and are capable of
modifying, its total idea. But if the experiment is varied in the
way that a complex image is divided into halves and one of these
presented at one moment, the other after a small but noticeable
interval, it is found that the two successive impressions cannot
be at all combined, as were the simultaneously given constituents.
If the two half-images, a and b, are compared with the total
image, a + b, shown in a later experiment, one of two things
may happen. Where the complexity of the impression is con-
siderable, it may simply not be seen that a + b is identical with
the sum of the successive ideas a and b. Or, if the identity is
recognised, it is clearly perceived that reflection and thought
have taken the place of direct observation. Suppose, for
instance, that the first impression given is that of a uniform
duodecagon. If the same object is shown again in a second
experiment, it will be at once recognised and clearly distin-
guished from a decagon, although there can have been no count-
ing of the angles, and although nothing is otherwise known as
to their number. Now suppose that in a second series of
experiments there are presented first one half of the duo-
decagon, then its other half, and thirdly the complete figure.
No one will obtain from the perception of these three objects
the idea that the two first together made up the last. That is
to say, our subjective perception marks off as totally distinct
processes the immediate and perceptual recognition, and the
mediate and logical recognition of a compound idea. The
former is an instantaneous process of perception, the latter a

260 Lectures on Human and Animal Psychology

serial process of comparative judgment. With the former,
again, is bound up a characteristic feeling, — an unfailing con-
stituent of perceptual recognitive processes to which we shall
recur later ; whereas the latter shows no trace of it.

These invariable and obvious characteristics of immediate
recognition, which are, of course, not confined exclusively to the
ideas of sight, lurnish us with a means of answering the general
question as to the range of consciousness. For immediate
recognition it is necessary that the recognised idea has, at some
time or another, been present in consciousness as a whole. The
problem, then, will now be to determine how many separate
ideas may be combined in ? total image without doing away
with the possibility of an unfailing perceptual recognition when
the same impression is repeated. The separate ideas which are
thus connected into a complex need not necessarily come from
impressions which are objectively simultaneous. Suppose, for
instance, that a number of auditory impressions be given in
fairly quick succession. The series forms a total impression, of
whose constituents there are certainly more than one in con-
sciousness at any moment. Thus we should obviously be quite
unable to estimate the rapidity at which one hammer-stroke in
a series followed another, if there were not present in conscious-
ness at the instant when a new sound comes one or more of
those preceding it ; if, that is, the time-intervals between every
two strokes were not directly given in perception. You can
see that the same conditions will hold for the perceptual com-
parison of different series of this kind "as hold for other
complex impressions. It is only what has been present in con-
sciousness at sometime or other as a whole that can be a unity
for perception, and as such a unity compared with another
similar whole. And there are special reasons for preferring
auditory impressions to those of other sense-stimuli in our
present investigation. In the first place, it is particularly easy to
obtain a relative simplicity and uniformity of sound-impressions.
Secondly, the sense of sight, the only possible rival of that of
hearing, is liable to disturbance owing to the differences between
direct and indirect vision. Lastly, we have had most practice
in the apprehension of uniform series of auditory impressions ;
so that it is easiest for us in their case to perform the act of

Range of Consciousness

261

recognition at once, and with the necessary certainty. You can
see for yourselves how experiments can be carried out. The
very simple technique of such experimentation is shown in Fig.
39. It requires a metronome, ?«, of the kind generally used for
marking time in music. Metronome-strokes will serve as the

FIG. 39-

simple ideas, the maximal number of which in consciousness we
have to determine. Affixed to the pendulum of the metronome
is a small iron plate, projecting on either side. This is arranged
between two electro-magnets, ^ and *2, in such a way that the
pendulum can be arrested or set swinging at any moment by
the closing or opening of a current passing through them from the
battery k±. The current is made by simply closing the key s with
the left hand. In order to mark off for perception the separate
series of metronome-beats, we make use of a small electric bell,^,
supplied by a second current, kz. This current is made for a
moment, and then broken again by an instantaneous pressure
upon the button of the telegraph key t. The experiments are
carried out as follows : a signal is given to the observer that
all is ready ; and then the experimenter opens s, and lets the

262 Lectures on Hziman and Animal Psychology

pendulum swing. Simultaneously with the first stroke, he
presses t, and the bell sounds. After the right number of strokes
has been given, a second series is at once begun, its first stroke
being again marked by a simultaneous bell- stroke. As soon as
the second series is concluded, the experiment is brought to an
end by closing s ; i.e., by the arrest of the pendulum by one of
the two electro-magnets. If we denote the metronome-strokes by
quavers, and the bell-signal by an accent placed above them,
an experiment consisting of two successive series may be repre-
sented in this way : —

rr

In this instance, the two series are of equal length. In actual
experimentation the second series is made to contain one stroke
more or less than the first ; while the length of the series and
the rapidity of the pendular oscillations will also be varied.
The pendulum can, of course, be slowed or quickened within
limits wide enough for the present purpose by moving the
running weight up or down. The problem, then, is to ascertain
how long a series may be, at a given rapidity of vibration, for
the immediately following series to be cognised as equal when
equal, and as unequal when unequal, without there being any
counting of the strokes. And a further question is how the
length of the just recognisable series varies with variation of
the rapidity of vibration.

A circumstance which facilitates these experiments, and tells
at the same time very strongly for the correctness of the
interpretation which we ascribe to them, is this : that the point
at which immediate recognition ceases to be possible can be
very accurately indicated by the observer. This point is really
settled at the conclusion of the first series ; for the series
is either apprehended directly as a coherent whole, or, if the
limit is past, appears as a discrete and indeterminate impression.
Peculiar feelings are connected with both phenomena, feelings
of distinctly opposite character, which make the observer fairly
certain at the beginning of the second series whether he will
be able to institute any comparison at all between the coming
group and that which has just ended. The most favourable

Range of Consciousness 263

objective conditions for the apprehension of the largest pos-
sible number of impressions are obtained when the interval
between every two strokes is o*2"-O'3". The number decreases
if the pendulum moves more quickly or more slowly ; and
grouping ceases to be possible at a lower limit of O'l", and at
an upper of about 4". Particularly interesting are the sub-
jective impressions in the neighbourhood of the upper limit.
You recall in this case the previous strokes as each new one
comes, but your recollection is accompanied very plainly by the
same feeling of cognition that you have when you recall pre-
vious ideas which have disappeared from consciousness. Each
single stroke, that is, stands to the foregoing one as (where
grouping is possible) each whole series stands to the preceding
series.

Within the limits of the possibility of conscious grouping
there comes to light a further phenomenon which is so variable
that it exercises a decisive influence on the result. If we give
ourselves quietly up to the apprehension of the impressions,
we observe that the separate strokes are not all alike, even
though they are really and objectively perfectly equal. We
alternately accentuate and slur them, just as we do in marking
time in speech, by a voluntary and regularly alternating in-
tensity of accentuation. If we denote the accented impressions
by points placed above them, we have the two series of our
former figure as they usually occur in reality : —

X /

i r i i i i i i i > i i i i i i i i i r i i i i

LJ LJ LJ LJ LJ LJ U LJ •_ — LJ LJ

The series of twelve strokes, that is, consists not of twelve
equivalent ideas, but of six ideas, each of which has two parts.
With this simplest form of accentuation we are able to group
into a recognisable series at most sixteen single strokes ; i.e.,
eight bimembral ideas.

But the same phenomenon may show itself in more com-
plicated form. The series need not be divided on this simplest
scheme in 2 : 8 time. There may be different degrees of
accentuation regularly alternating with one another and with
slurs ; and so there may arise a more complicated rhythm.
There need not be any intention to form these secondar)

264 Lectures on Htiman and Animal Psychology

groups : a certain degree of complexity may result simply from
the effort to hold as many impressions as possible together
in consciousness. You may quite easily obtain the following
system, e.g., in which the different degrees of accentuation are
again denoted by points, the strongest by three, the next by
two, and the weakest by one, —

and so on. By employing this graduated accentuation, we
divide up the total idea of the current series into component
ideas, each of eight single impressions.

Detailed and varied observations of this nature have shown
that we are able with strained attention to hold in mind, and
to compare with an immediately following group of similai
extent, a series consisting of five of these compound im-
pressions ; that is, of forty separate impressions. If the ideas
are made as little complex as possible, therefore, eight is the
maximum of grouping; if they are made as complex as possible,
five. But, on the other hand, the number of ideational elements
simultaneously present in consciousness may be raised through
progressive complexity from sixteen to forty.

We never find more than three accents employed to divide a
series, for the obvious reason that more than three cannot be
distinguished with certainty. This reminds us of the fact that
in other cases of purely quantitative discrimination in im-
mediate sensation we cannot pass beyond the three-limit
without imperilling the accuracy of recognition. We can easily
interpolate a sound of mean intensity between a stronger and a
weaker, but hardly more. Ordinary language designates grey
as an intermediate quality between black and white ; and grey
itself is further distinguished as dark grey, grey, and bright
grey. This limitation of our capacity to graduate quantitatively
may well be referred to that principle of relativity which
underlies mental measurement in general (cf. pp. 62, 63). The
principle tells us that any estimation of intensive magnitude
must be made in terms of other magnitudes simultaneously
ideated. So that we can easily apprehend a given sensation in
its relation to a stronger and a weaker, but are hopelessly at

Range of Consciousness 265

sea when required to hold in mind any larger number of sensible
relations.

If we look at the metrical forms employed in music and
poetry, we find again that the limit of three degrees of accent
is never exceeded. The absolute amount of accentuation may,
of course, be very different in different cases. But in immediate
perception these different degrees are always arranged in three
principal classes, which alone are of any real importance in
metrical division as a basis of classification for rhythmical
forms. As a matter of fact, however, music and poetry never
push their use of this aid in the formation of easily compre-
hended ideational series to the extreme limit of conscious
grouping. Each member in a rhythmical series must be
referred to its predecessors ; and for this to be done with
pleasure and without effort, it is necessary that the grasp of
consciousness be not too heavily taxed. So that a time like
the 6 : 4 is one of the most complex of the rhythms employed
in music. Its scheme is the following : —

•

Lr Lr Lr 'Lr Lr. Lr •

It contains, you see, only twelve simple impressions. We must,
of course, remember that in this case there is present, beside
the intensive, a qualitative tone-variation, capable of far wider
variation and, therefore, setting all the narrower bounds to
intensive change.

LECTURE XVIII

§ I. TEMPORAL COURSE OF IDEAS. § II. THE PERSONAL DIFFERENCE
OF ASTRONOMERS ; EYE AND EAR METHOD. § III. METHOD OF
REGISTRATION. § IV. REACTION-TIME. § V. TEMPORAL DETERMINA-
TION OF MENTAL PROCESSES.

§ I

WE have solved the problem of determining the Ideational
content of consciousness at any given moment. The
next question that arises is that of ideational succession.
This falls into two parts : we must investigate, first, the time-
relations of ideational change, and, secondly, the qualitative
relations obtaining between the changing ideas. The actual
train of ideas must always be regarded under both its temporal
and qualitative aspects. A quantitative consideration of its
time-relations cannot, therefore, neglect the qualitative relations
of the single ideas, just because mental time-relations in general
must be essentially dependent upon the quality of conscious
content. At the same time, we shall find it best to separate the
two sides of the problem so far, at least, as to deal predomi-
nantly with temporal properties, and to attend only to those
more general and fundamental qualitative relations which
exercise a decisive influence upon them.

The coming and going, the rise and fall, of ideas have been
often enough described, though a guarantee for the absolute
correctness of the description cannot always be found. The
alleged facts rest partly upon all manner of speculative assump-
tions, partly on the uncertain ground of introspection. Intro-
spection unsupported by experiment can just as little lead to
any certain result here as it could in the inquiry regarding the
range of consciousness. And, unfortunately, the phenomena of
ideational succession with which introspection was specially

concerned happened to be just those which are least of all

266

The Personal Difference of Astronomers 267

accessible to exact investigation, — the internal train of fancy and
memory-images which we find running its course in the absence
of external sense-perceptions. There was total disregard of
the ideas directly excited by sense-impressions, or directly and
uniformly connected with sense-perceptions. In their case there
seemed to be no need of question, inasmuch as in sense-percep-
tion the course of objective impressions and the train of subjec-
tive ideas were entirely congruent.

§ II

The first indication of the wrongness of this opinion, and the
first sign that the shortest and indeed the only road to the in-
vestigation of the temporal course of conscious processes lay in
observing the ideas directly aroused by external stimuli, came
to psychology from outside, from a science in which obser-
vational methods had come in the course of time to a high
development, — astronomy. Astronomers had noticed certain
sources of error in the temporal determination of movements of
the heavenly bodies which, while they tended to invalidate the
objective value of an observation, cast at the same time a most
instructive light upon the subjective peculiarities of the observer.

Suppose that we have to determine the time of the passage
of a star at some distance from the pole across the meridian.
We may employ an old astronomical method, which is still
sometimes used for temporal determinations, and which is called
the ' eye and ear method.' A little before the time of the ex-
pected passage, the astronomer sets his telescope, in the eye-
piece of which there have been fixed a number of clearly visible
vertical threads, in such a way that the middle thread exactly
coincides with the meridian of the part of the sky under obser-
vation. Before looking through the instrument, he notes the
time by the astronomical clock at his side, and then goes on
counting the pendulum-beats while he follows the movement of
the star. Now the time-determination would be very simple, if
a pendulum-beat came at the precise moment at which the star
crosses the middle thread. But that, of course, happens only
occasionally and by chance : as a rule, the passage occurs in the
interval between two beats. To ascertain the exact time of the
passage, therefore, it is necessary to determine how much time-

268 Lectures on Human and Animal Psychology

has elapsed between the last beat before the passage and the
passage itself, and to add this time, — some fraction of a second,
— to the time of the last beat. The observer notes, therefore,
the position of the star at the beat directly before its passage
across the middle thread, and also its position at the beat which
f $ comes immediately after the passage, and
then divides the time according to the
length of space traversed. If f (Fig. 40)
is the middle thread of the telescope, a
the position of the star at the first beat
and b at the second, and if a f is, e.g.,
Fi«- 4°- twice as long as f b, there must be added

f" to the last counted second. ;

When the errors dependent upon accidental circumstances
have all been eliminated, these measurements still show differ-
ences between different observers. They persist even when
there is no external reason discoverable. The fact was first
noticed in the annals of the Greenwich Observatory for 1795.
The astronomer writes that he dismissed his assistant as un-
reliable because he had acquired the habit of seeing all stellar
transits half a second too late. Not till many decades later was
the scientific honour of the assistant vindicated. It was the
celebrated German astronomer Bessel who proved that this
difference between two observers is only a special case of a
phenomenon of universal occurrence. Bessel compared his own
results with those of other astronomers, and came to the sur-
prising conclusion that it is hardly possible to find two observers
who put the passage of a star at precisely the same time, and
that the personal differences may amount to a whole second.
These observations were confirmed at all observatories, and in
the course of the experiments many other interesting facts came
to light. It was found, for instance, that the personal difference
between two observers is a variable quantity, fluctuating, as a
rule, but little in short periods of time, but showing larger vari-
ations in the course of months and years.

It is plain that these differences could not possibly occur if
the idea of an impression and the impression itself came simul-
taneously. It is true that differences might appear between the
determinations of various observers owing- to uneliminaHe

The Personal Difference of Astronomers 269

errors of measurement, but these would disappear if a sufficient
number of observations were taken. A constant and regular
difference, such as this actually is, is only explicable on the
assumption that the objective times of the auditory and visual
impression and the times of their subjective perception are not
identical, and that these times show a further difference from
one another according to the individual observer Now attention
will obviously exercise a decisive influence upon the direction
and magnitude of such individual variations. Suppose that one
observer is attending more closely to the visual impression of
the star. A relatively longer time will a c f b /?

elapse before the apperception of the
sound of the pendulum-beat. If, there-
fore, the real position of the star is a
at the first beat and b at the second
(Fig. 41), the sound will possibly not I
be apperceived till c and d, so that FIG. 41.

these appear to be the two positions of the star. If a c and b d
are each of them jr", the passage of the star is plainly put •£"
later than it really should be. On the other hand, if the atten-
tion is concentrated principally on the pendulum-beats, it will
be fully ready and properly adjusted for these, coming as they
do in regular succession, before they actually enter conscious-
ness. Hence it may happen that the beat of the pendulum is
associated with some point of time earlier than the exact
moment of the star's passage across the meridian. In this case
you hear too early, so to speak, just c a f d I

as in the other case you heard too late.
The positions c and d (Fig. 42) are now
inversely related to a and b. If c a and
d b are again •£•", the passage is put
^" earlier than it really occurs. If
we imagine that one of two astronomers FIG. 42.

observes on the scheme of Fig. 41, the other on that of Fig. 42, —
in other words, that the attention of the one is predominantly
visual, that of the other predominantly auditory, — there will be
a constant personal difference between them of -|" — ^". You
can also see that the smaller differences will appear where the
manner of observing is the same in both cases, but there are

270 Lectures on Human and Animal Psychology

differences in the degree of the strain of the attention ; while
the larger differences must point to differences like those just
described, in the direction of the attention.

It is, unfortunately, not possible in these astronomical obser-
vations to eliminate the errors introduced by the mental ten-
dencies of the observer. We do not know the time of the actual
passage of the star, and we can only infer from the personal
differences that the observed time of passage is not the real
time. But the exact deviation of the individual observer from
the true time remains undetermined. Hence the explanation
which we have offered for personal differences in general and
the larger ones in particular is so far no more than a hypothesis.
To prove that it is right, we should have to determine the actual
position of the star at some point in its passage and compare
this with the estimated position given by different observers.
This is, of course, impossible ; the heavenly bodies are beyond
our control. But there is nothing to prevent the repetition of
the phenomenon by artificial means under circumstances which
readily allow of a comparison of actual and estimated times. A
very simple apparatus of this description is represented in Fig.

43. It is the one by the aid
of which I carried out my

first experiments on the time-
relations of mental processes
in 1861. It consists of a large,
heavy wooden pendulum. The
bulb carries a pointer, which,
as the pendulum swings, passes
over a circular scale. Near
the point of rotation m there
is fixed to the stem a hori-
zontal metal bar : s s. A
movable, vertical standard, k,
has attached to it a small metal spring, also in the horizontal
line. The spring is fixed in such a way that the bar s s in
passing by produces a single short click, the end of the bar and
the point of the spring just touching each other, while the shock
is so slight that the course of the heavy pendulum is not notice-
ably affected. By watching the course of the pointer attached

Tke Personal Difference of Astronomers 271

to the bulb of the pendulum, while the upper part of the instru-
ment remains concealed, we can determine at what point of its
passage to or fro the click of the spring takes place. For
example, if the pointer appears to be at e' at the moment of
the sound, the bar s s will be in the position a b, and this will
mean that the passage is put too early. If the pointer seemed
to be at e", the bar would be in the position c d> and this would
mean that the passage was put too late. If we know the dura-
tion and amplitude of the pendular vibration, and measure the
angular difference between e' or e" and the actual point at
which the bar s s comes in contact with the spring, we can
easily calculate the interval between the giving of the sound
and its apperception. To obviate the influence of preconceived
judgments, the spring is given a slightly different position in
each experiment, so that the observer never knows when the
sound is really coming. It was found by this method of inves-
tigation that a slow vibration-rate gave a time-displacement
averaging £". The time of the click was put that much too
early ; the sound-impression was associated with the position of
the pointer, which in actual fact preceded it by ^". Later
experiments with a more adequate technique * have shown that
the magnitude and direction of this time-displacement are con-
ditioned in the most various ways. Of especial importance is
the rapidity at which the sound-impressions succeed one another.
In a slow series we tend to antedate the passage, in a rapid
series to postdate it. Moreover, the temporal localisation of the
sound becomes later if other impressions, — e.g., electrical cuta-
neous stimuli, — are given simultaneously with it. The nature of
these influences confirms the explanation of the varying time-
displacement in astronomical observations offered above. For
all the conditions which delay our apprehension of the passage
are conditions which either prevent or retard the completion of
a preparatory adjustment of the attention. To the former class
belongs a high rapidity of the succession of sound-impressions ;
to the latter, the simultaneous excitation of other senses.

1 1 have described and figured the apparatus, under the name of Pendel-
apparat fur Komplikationsversuche, in my Physioi. Psych., 3rd ed., ii., p.
344-

272 Lectures on Human and Animal Psychology

§ HI

But however interesting these astronomical observations and
the psychological experiments by the eye and ear method
modelled upon them may be for a theory of attention, they
give us no direct information with regard to the duration of
mental processes. It would be altogether wrong to take the
absolute difference between the actual and estimated time of
the passage for a time-period corresponding to the duration of
any particular mental act. For we have seen that this difference
simply depends on the interrelation of the objective change of
impressions and the variation in attentional adjustment. It will
be positive, negative, or zero, according to the experimental
conditions ; the latter, of course, when the rate of succession is
found at which the actual and apparent times of passage are
approximately coincident.

But there is another method which has brought us nearer the
desired result. Like the first, it has come to psychology from
astronomy. To avoid the considerable personal differences of
the eye and ear method, and at the same time to obtain greater
accuracy in the estimated times of stellar transits, the astrono-
mers have recently been led to prefer a different mode of pro-
cedure, which is called the registration-method. The passage
of the star across the field of the telescope is observed in precisely
the same way as before, except that there is no counting of pen-
dulum-beats. At the moment when the star passes the meridian
thread, a movement of the hand is made, which records the
transit upon a chronometrical instrument. The apparatus em-
ployed is usually as follows : — an endless sheet of paper is
transferred by clockwork from one cylinder to another, so as to
move at a constant velocity before a twofold registration instru-
ment One half of this consists in a writing lever, which is
moved by an electro-magnet every time that the pendulum of
the clock swings through its position of rest. If the pendulum
makes one complete to-and-fro movement in the second, the
lever moves every half-second, making a momentary elevation
in the line it is describing upon the moving sheet of paper (u u',
Fig. 44). The other half of the registration instrument consists in
a similar writing lever, which is connected with a key of the

Method of Registration 273

kind used in telegraphy. The observer keeps this key closed by
pressure of the hand, and opens it at the moment when the star
crosses the middle thread of the telescope. A movement of the
lever follows, the beginning of which can be exactly determined
from the simultaneously recorded half-seconds of the pendulum.
Thus, if U U' is the half-second line upon the moving paper, and
R R' the line recording the reaction-movement of the observer's
hand, we can ascertain the time at which the second lever began
to rise, c, by drawing a perpendicular, c b, to the line u u, and
measuring the time a b which has elapsed between b and the
beginning of the last half-second. This is done, again, by putting
space for time: if a b = ^a a, %" must be added to the time-
value of a.

FIG. 44.

Astronomical observations of stellar transits by the registration-
method showed, as had been expected, smaller personal dif-
ferences than those of the eye and ear method. But the differences
by no means disappeared. They may still amount to hun-
dredths or even tenths of a second. And this is not difficult to
understand. We cannot suppose that the reacting hand-move-
ment takes place simultaneously with the actual passage of the
star: a certain time will elapse between the transit and its
perception, and again between the perception and the execution
of the movement, which may possibly be different in different
individuals, and so condition ' personal differences.' Indeed, the
composition of these lesser time-values is plainly a matter of
more complexity than that of the times found by the eye and ear
method. In the first place, physiological processes occupying
a certain period of time enter into the total movement-process
under consideration. The impression of the star upon the
meridian thread must be conducted to the brain, must arouse an
excitation there ; and then, before the hand-movement can take
place, the impulse of will must be conveyed to the muscles, and

T

274 Lectures on Human and Animal Psychology

these stimulated to contract. To these two purely physiological
must be added the psychological or psychophysical processes of
apperception of the impression and impulse of will. Even
though in actions like this, where the movement answering to
the impression is so accurately anticipated, the two acts of appre-
hension and corresponding movement may possibly be exactly
coincident in time, still it seems necessary to suppose that this
whole psychophysical process will occupy no inconsiderable, per-
haps the major, part of the total time elapsing between sense-
impression and reaction-movement. The supposition becomes
probability when we take into account the magnitude of the
personal differences which are still found to occur. Differences
so large as these may be expected where the processes involved
are mental, but hardly where they are physiological and simi-
larly conditioned. But neither does the registration-method tell
us anything of the actual time-values of the various processes.
We do not know the real time of the stellar transit, and so are

S
E

FIG. 45.

still restricted to the inference that, since the differences between
separate observers are so considerable, the times whose dif-
ferences they are must themselves be comparatively large.

But here, again, it is not difficult to introduce artificial experi-
mental conditions which allow of the measurement of the
absolute times in question. We can use for this purpose the
same astronomical method, with the single difference that, in
addition to the instruments for registering time and movement,
there is introduced a third lever to mark upon the moving paper
the moment at which the external sense-stimulus is given. It is
also advantageous, since the times and time-differences to be de-
termined may possibly be very snvall, to substitute for the vibra-
tions of a clock-pendulum in the record of the time-curve some
other and more accurate chronometrical instrument. The best
is a vibrating tuning-fork ; and the technique is so far simplified
that a tuning-fork with a bristle attached to it can very well

Method of Registration 275

trace its own movements. For instance, if ^ S in Fig. 45 denotes
the line written by the vibrating fork, and R R' that of the hand-
reaction, a third line, E E', between the two, will represent the
self-registration by the stimulus of the moment of its objective
occurrence. From the beginning of the elevation indicating the
giving of the stimulus and from the beginning of the reaction-
movement answering to it, perpendiculars, a b and c d, are drawn
to the tuning-fork curve, and the time between b and d measured
by reference to the known duration of its vibrations. If, e.g., the
fork makes loo vibrations in i", — a hundred full vibrations, each
comprising one hill and one valley of the record, — -every tenth
part of a to-and-fro movement corresponds to yuW'' a sPace"
value which is not too small to admit of fairly accurate measure-
ment. The distance b d would then correspond to some
"fw ~T£W$ or O'JO4"' The time thus measured between im-
pression and reaction-movement is called the reaction-time. It
is made up, as we have seen, of purely physiological and of
psychological processes ; and we cannot separate the two, or
ascertain with even conjectural probability the time-value of the
mental component. But although the mere determination of
the reaction-time possesses scarcely any importance for psy-
chology, it, nevertheless, is the necessary first step in all possible
mental time-measurements. Recognising this, we are bound to
consider it in some little detail.

Since the reaction-time may in certain circumstances amount
too' i — o-2",but the time- values of the mental processes connected
with it and approached by means of it often be considerably
larger, this method of counting the vibrations of the tuning-fork
becomes too cumbrous and tedious for experimental use.
There is generally substituted for it an apparatus of more recent
construction, which works as follows : the vibrating body does
not record its movement upon paper, but regulates the course of
a very rapidly running clockwork. A vibrating spring, which
takes the place of the less convenient tuning-fork, interlocks
with a toothed clock-wheel in such a way that at each vibration
the wheel can only turn by the width of one tooth. The same
wheel is connected with a clock-face, on which the times that
have elapsed can be directly read off. To allow of the measure-
ment of longer periods, connections are introduced in the .wheel-

276 Lectures on Hitman and Animal Psychology

work of the clock similar to those which in an ordinary seconds
watch join the wheel that carries the seconds hand with that
regulating the large hand. There is further introduced a system
of electro-magnets, which enables us to arrest or start the move-
ment of the hand at any moment by the make or break of a
current. It is now easy to arrange the experiment in such a
way that the giving of the external sense-impression sets the
clock in movement, and the reaction of the observer stops it.
The difference between the position of the hand before and after
gives us the reaction-time.

§ IV

In making experiments of this kind with chronometrical in-
struments, or drawing inferences from experiments, we must
remember that the chronoscope, whose unit is a thousandth of
a second, cannot be regarded as a simple watch. It would be
quite wrong to read off the times from it without paying regard
to the numerous sources of error which minute chronometry
always involves. Unless the apparatus is continually and ac-
curately tested, and the observer thoroughly practised in the
technique of such experimentation, there can be no hope of
obtaining reliable results. And you will find during the course
of practice that there are individuals who are entirely incapable
of any steady concentration of the attention, and who will, there-
fore, never make trustworthy subjects. That should not be
surprising. It is not every one who has the capacity for astro-
nomical or physical observation ; and it is not to be expected
either that every one is endowed with the gifts requisite for
psychological experimentation. This is, unfortunately, not
seldom forgotten. And the consequence is, that the literature
of psychological chronometry, which has assumed such imposing,
dimensions in the course of the last few years, gives but ? scanty
store of sifted grain to the inquirer who would turn it to psy-
chological account.

At the same time, the simple reactions to impressions of
sound, light, and touch are happily possessed of certain charac-
teristics which render it an easy matter to separate the useful
from the useless, provided only that the experiments are de-
scribed in sufficient detail to allow of their being definitely

Reaction- time 277

known. The first consists in the mean value of the reaction-
time, the second in the relative constancy of this value. In
opposition to all the earlier statements of large individual
differences in reaction-time, it has been shown with ever-increas-
ing certainty since the introduction of the more accurate obser-
vational methods that, other conditions equal, there is great
uniformity in reaction-time, — a uniformity which is independent
of all individual differences when once practice has been carried
sufficiently far. Equality of conditions means, first, likeness of
quality and intensity of the sense-impression, and, secondly,
likeness in the condition of the sensory and motor apparatus
concerned in the reaction-process. As regards the former point,
it is noteworthy that the different sense-departments show cer-
tain constant differences, and that very weak stimuli lengthen
the times, though these are absolutely constant for impressions
of moderate intensity ; as regards the second, that the condi-
tion of the organs of sense and movement, however uniform
their functioning, never fails to present one difference, which is
determined by differences in the direction of the attention, and
therefore so far psychophysical in nature. The attention may
be principally directed upon the expected sense-impression.
In this case the specific muscular apparatus of the sense-organ
(e.g., the tensor ty'mpani, or the muscles of accommodation) are
strongly innervated, the muscles concerned in the reaction-
movement only weakly. Or the attention may be mainly
turned to the movement which is to be made. In this case the
energy of innervation is distributed in the converse way. We
may, therefore, designate the first kind of reaction, where the
sense-organ is attended to, the sensorial form ; the second, where
the attention is directed upon the organs of movement, the
muscular. No one, then, can be regarded as capable of experi-
menting upon the time-relations of mental processes until he is
able to change at will from either of these forms of reaction to
the other. The question as to which form we have in a parti-
cular case can be easily answered by reference to the magnitude
of the measured times and the degree of their average constancy.
If we take as our time-unit, for simplicity's sake, not the second,
but the thousandth part of a second, and denote this unit by
the Greek letter <r (sigma) written above the line, we may put

278 Lectures on Human and Animal Psychology

it that the sensorial reaction amounts to 210 — 290^, the muscular
to no — 180^. The smaller number in each case gives the time
for touch and hearing, the larger for that of sight. The mean
variation of the separate experiments in an experimental series
of at least 25 observations amounts in the first case to 20 — 40^
(where again the larger number refers to the sense of sight),
in the second to 10 — 20°". Whenever, owing to insufficient
practice or general inability to concentrate the attention, there
is oscillation between the two kinds of reaction, or neither is
attained in its extreme form, we find differences in the dura-
tion of the average values and (what is a still less mistakable
indication) in the magnitude of the mean variation.

§ V

We may designate this kind of reaction to an expected im-
pression of sound, touch, or light the simple reaction. In each
of its forms it may be regarded, for the reasons given above, as
a composite process, containing both physiological and psycho-
logical constituents. And the association of these constituents
is so difficult of analysis that no conclusion can be drawn re-
garding the duration of the mental terms of the series. But in
our consciousness these mental terms are separated off from the
others : and we may evidently insert other mental acts in the
same process, and so lengthen the total time of reaction by the
precise interval which they require for their completion. Such
reactions we may call compound. And we shall obtain the dura-
tion of the interpolated mental process by subtracting the simple
from the compound time. For we may surely assume that the
purely physiological processes are the same in both cases ; and
that the apprehension of the impression and the impulse of will,
implied in the simple reaction, recur in similar form in the
compound. There is always one necessary condition, it is true :
that the sensorial form be taken as the basis of comparison, and
not the muscular ; the muscular is so automatic in character
that the interpolation of new mental processes is impossible.
For instance, in a first experimental series the observer may
react to some light-impression without regarding its qualitative
character, the reaction-movement simply following the impres-
sion upon the eye. In a second series qualitatively different

Temporal Determination of Mental Processes 279

light-impressions may be presented irregularly and at random,
and the observer required only to react after he has distinguished
the quality of the particular impression. By subtracting the
previously determined simple time from this longer time we get
a discrimination-time ; that is, the time required to complete an V
act of discrimination.

But now we can easily go a step farther. We may require
the observer after discrimination to choose between different
reaction-movements, and not to react until he has chosen. Thus
two light-impressions, say a red and a blue, may be given in
irregular order, the rubric being that red shall be reacted to
with the right hand and blue with the left. Here, you see,
there are two mental acts over and beyond the simple reaction, —
first, the act of discrimination as before ; and secondly, a new
process, that of choice between two actions. If we subtract the
compound time of the first order, — the discrimination-time, —
from the compound time of the second order, — the time of dis-
crimination with choice, — we obtain a simple choice time. Besides \j
this, we may obtain compound choice times ; i.e., the duration of
the act of choice between more than two movements. Since
we have ten fingers at our disposal for experimental purposes,
we can prescribe choice between as many as ten movements.
In this case, of course, the association between the ten-finger
movements and ten qualitatively different associations must
have been made stable by practice, if the conditions of the ex-
periment are to resemble those of simple choice in everything
except the number of impressions. Impressions which are to
be discriminated only may, naturally, be varied to a very much
greater degree. We can determine the visual discrimination-
times, for instance, not only of colours and brightnesses, but also
of letters, words, geometrical figures, and other more or less
well-known objects.

Yet another method of obtaining reaction-times of the second
order is to set out from the time of discrimination or cognition,
and to require that the reaction-movement shall follow only
when some idea has been associated to the idea aroused by the
impression. By subtracting again the cognition reaction from
the total association reaction, we obtain an association-time ; that v
is, the time required for the appearance in consciousness of an

280 Lectures on Hitman and Animal Psychology

associated idea excited by a perception. You will see at once
that here again the conditions can be varied at will, whether by
limiting the association to definite groups of ideas, by requiring
the completion of trains of logical thought suggested by the
sense-perception, or what not.

We cannot, of course, enter in this place into the details of
these measurements. Here is a brief table of figures which
give the average time-value of some of the above-mentioned
mental processes in thousandths of a second * : —

Cognition of a colour .... 30

„ „ a short word ... 50

Choice between 2 movements . . 80

10 „ ... 400

Association 300 — 800

A simple geometrical figure (triangle, square, etc.), or any
other equally simple visual object, seems to be cognised almost
as quickly as a simple colour. A single letter requires about
the same time as a short word. Both these facts show the im-
mense influence of habitual practice. The total impression of a
well-known object is so familiar to us, that the need of analysing
it into its constituents in order to distinguish it from other ob-
jects is as remote as is the possibility of such analysis in the
case of a simple colour. In the same way, when once we have
learned to read, we do not divide up a word into its component
letters, but apprehend it as a single total impression. And there
belongs here a further observation of interest. A letter printed
in the ordinary German type requires 10 — 20°" more for its cogni-

1 The two first lines of this table are taken from the results of an investi-
gation recently carried out in my Institute by E. B. Titchener (Phil. Studien,
vol. viii., part i). They are very much smaller than the. values ascribed to
the same acts in earlier researches, and published in the 3rd edition of my
Physiol. Psychologic. The reason for the difference is the more careful
observation of a uniformly sensorial form of reaction, both in the discrimina-
tion-experiments and the simple times with which they were compared.
The earlier numbers were gained in experiments made before the discovery
and consequent utilising of the difference between the two simple forms, and
by observers who inclined to react muscularly, — a circumstance which in-
creased their cognition-times by something like the difference between the
sensorial and muscular forms ; i.e., by about 80 — 100°".

Temporal Determination of Mental Processes 281

tion than a letter of the same size in the Roman character. But
there is no such difference between words printed in the two
types : the German word can be read in just about the same
time as the Roman. The single German letter is harder to
cognise, because of all its fine strokes and flourishes. You can
see this very easily if you take the capitals ; now and again
there occurs a word printed throughout in large letters. It is
true that cognition is also retarded in this case by the un-
accustomed nature of the whole impression. And the same
factor is operative to make us slower in reading substantives
printed or written in Grimm's way with small first letters, — a fact
which tells against the advisability of riding this Germanistic
hobby.

We can easily understand why the times of the cognition of r
complex objects, of association and of the formation of judg-
ments, should be, not only longer, but at the same time more
variable, than the others. The more complicated the processes
become, the more dependent is each particular result upon the
individual conditions of observation, and especially upon the
disposition of the observer, itself determined by numberless
past experiences and incalculable chances. A further general
conclusion to be drawn from the numbers in the table is, that /
the duration of mental processes is by no means so brief as has +J
often been assumed. The phrase ' quick as thought ' does not
refer so much to the actual rapidity with which idea succeeds
idea in consciousness, as to our undoubted ability to drop out
the intermediate terms in a train of thought, and so pass at one
bound from the first to the last link in the ideational chain.
Apart from this, it is obvious that the absolute time-values of
the various mental processes are of no importance whatsoever
in themselves ; they only become important when they help to
throw light upon the nature and interconnection of our ' states
of mind.' And for this reason the quantitative examination of
the temporal course of ideas must always go hand in hand with
the qualitative investigation of their mutual relations. If it pays
heed to these facts, the psychological chronometry of the
future may be looked to for the solution of many an important
problem.

LECTURE XIX

§ I. QUALITATIVE CHANGE OF IDEAS. § II. ASSOCIATION OF IDEAS r
SIMULTANEOUS ASSOCIATION ; COMPLICATION. §111. ASSIMILATION..
§ IV. THEORY OF SIMULTANEOUS ASSOCIATION.

IF we look for a moment at the coming and going of ideas in
our minds, we cannot fail to see that the plot of the play
is determined by two influences, — accidental external sense-
impressions and previous experiences. Which of the two pre-
ponderates at a particular time depends upon circumstances.
Cast your eye over a landscape, or follow attentively the render-
ing of a musical composition, and you will find yourselves
seemingly wholly given up to the external impressions ; subjec-
tive tendencies coming in only secondarily, and rather as feelings
than as ideas. Now try to recall the events of the past few days.
External sense-impressions are hardly noticed ; and the train
of ideas, so far as it is clear and distinct, consists solely of
reproductions of previous mental experiences. These are both
extreme cases ; ordinarily we find ourselves in some intermediate
frame of mind. Memory-ideas art aroused by sense-perceptions,
and again interrupted by new impressions. Wherever the in-
fluence of past experience is traceable, we find the memory-
ideas aroused evidencing a definite relation to the condition
of consciousness at the time. Sense-perception varies with
every variation of the environment ; but the memory-image is
always suggested, whether by a sense-perception or a previous
memory-image. You will object that now and again a recollection
crops up suddenly and for no apparent reason. But attentive
introspection will in most of these cases enable you to discover
the thread of connection with your present state of mind.
However little obvious this connection, then, we may safely

Association of Ideas

assume that it is there. If it escapes our observation altogether,
as it may do, that is only because the conditions are not favour-
able for its apprehension.

The interconnections of memory-ideas and sense-perceptions,.
or of memory-ideas with other memory-ideas, are called associa-
tions of ideas. The term belongs to the English ' association '
psychology. It was first employed to cover the phenomena of
memory only, but afterwards extended to all possible connec-
tions of ideas originating in the preconditions of consciousness.
As customarily used, it is at once too narrow and too wide : too-
narrow because it leaves out of account a whole number of
connections for the sole reason that in them the ideas do not
come to consciousness in succession as in ordinary recollection,
but, owing to special conditions, appear simultaneously as a
complex totality ; too wide because it embraces all successive
ideational connections, the act of recollection aroused by a
simple sense-impression and the most involved process of logical
thought. Now, true as it may be that in both these cases the
ideational connection is determined by mutual relations implied
in past conscious experience, it is equally true that they are in-
all other respects so different that to treat of them without
further discrimination cannot but obscure the analysis of their
constituent processes and hinder the understanding of their
inter-relation. We shall ourselves mean by associations simply
those ideational connections which do not exhibit the charac-
teristics of the activity of logical thought. What these are we
shall discuss later.

§ H

The starting-point of the doctrine of association, in the usual
sense of the term, was observation of the reproduction of earlier
ideas. It has hardly done more than put into modern form
what had been taught as the psychology of memory from
Aristotle down. But conscious recollection implies a distinc-
tion between the inducing and the induced ideas ; if the two are
not discriminated, the process cannot be that of conscious recol-
lection. Now it is evident that this recognition of an idea as
having been previously experienced is a character which may

284 Lectures on Human and Animal Psychology

possibly attach to a revived idea, but need not by any means
necessarily do so. The simpler case of association we must
rather admit to be that in which ideas are connected simply by
reason of their mutual relations in consciousness, and without
there being any direct apprehension of the connection as an act
•of recollection. Certainly memory presupposes association, — on
the assumption, that is, that no idea comes into our minds with-
out cause, — but not every association involves an act of memory.
That is, we must obviously set out first of all from the phe-
nomena of association proper, and then go on to determine
what new conditions are necessary for the association to become
•recollection.

In this wider sense association embraces a whole number of
•connective processes in which the associated ideas do not suc-
ceed one another, but come to consciousness as a simultaneous
ideational complex. There can be no question here of an act
of recollection, for the simple reason that the induced idea
associated with the inducing is not in any sense separate from
it, — in other words, cannot be independently compared either
with it, or with any other idea. We may call connections of
this kind, in which the primary inducing and the associatively
induced idea form a simultaneous conscious complex, 'associa-
tions in simultaneous form,' or, for brevity's sake, simultaneous
associations. There belong here, in the first place, all those
products of the fusion of simple sensations which compose
our complex sense-perceptions. These latter always consist of
.a connection of several sensations forming a simultaneous com-
plex idea, such as a compound clang or some spatial idea of
sight or touch. One difference there is between these connec-

o

tions and other associations, — that the sense-impressions which
arouse the constituent sensations are themselves interconnected;
so that the re-excitation of earlier ideas, though of course not
entirely inhibited, is completely overshadowed by the con-
nective tendencies obtaining among the sensations. The sensa-
tions composing a clang or a visual perception depend upon a
simultaneous activity of sensory stimuli. At the same time
this difference does not imply any essential difference in the
psychological character of the general process ; that is, if we
.regard as the chief characteristic of association this property

Association of Ideas 285

of mind to connect certain ideas or ideational elements auto-
matically into a complex idea. And there is every reason for
doing this, since, surely, certain types of clang, certain spatial
arrangements of sensations, are every whit as familiar as, nay
even more familiar than is, for instance, the connection' of a
perception with a similar memory-image. But this means that
in these simultaneous associations of perception also there is
nothing to prevent a sensation-element which is not actually
given in the sense-impression being supplied by immediate
reproduction. We have seen, for instance, that eye-movement
influences the perception of visual space even when the organ i>
at rest ; thus we may be deceived as to the position or move-
ment of external objects in consequence of having intended, but
not actually executed, an ocular movement, and this just
because of the intimate association of movement-sensation with
impulse of will.1

These fusions of uniformly connected sensations, which con-
stitute sense-perception in general, are not very obviously
related to the ' associations ' of current psychology. More
akin to these are the interconnections of the perceptions of
different senses. We see a musical instrument, and hear a
clang from it. Our eye apprehends the white, crystalline nature
of a lump of sugar at the same time that our tongue is
experiencing a taste-sensation of the quality sweet. There
arises in this way a connection between sensations and percep-
tions of different senses so intimate, that if but one sense-
impression chances to be actually presented, or the memory-
image of an impression aroused in the domain of one sense
only, the other sensation is at once mentally associated with it.
We hear the piano, and no sooner do we hear it than a vague
visual image of the instrument crops up in our minds. Or we
taste sugar in the dark, and there is at once associated vvitli
its taste a general notion of what it looks like. These connec-
tions of ideas of disparate senses which are referred to the
same objects, and so belong closely together, we may term with
Herbart complications. There can be no doubt that they are
simultaneous associations. One sense-impression is so inti-

1 For similar instances cf. Lecture V. (Associations of Tone-sensations),
and Lectures IX. and X. (Associations of Spatial Perception).

286 Lectures on Human and Animal Psychology

.mately associated with another, or, at least, the origin of the
two is so little distinguishable in time, that the disparate
•constituents show themselves in consciousness only as the inter-
related parts of a single idea

Most frequent and most important among the complications
are verbal ideas. They stand, as a rule, in a twofold connec-
tion : the acoustical impression is associated, first, with a
sensation of movement, and then, secondly, — at least, in many
•cases, — with the visual impression of the printed or written
•characters. Movement-sensations are evidently complicated
-with other ideas as well. They acquire an especial significance
from the fact that the memory-image of a movement is apt
at once to arouse the movement itself. The consequence of
this is, that movement- sensations often act vicariously for the
sensations of certain senses whose memory-images are so faint,
that we either do not perceive them at all or only imperfectly
.and by the aid of the muscular sensations customarily asso-
ciated with them. It is, for instance, in most cases illusion
when you think that you can recall the scent of a rose.
Observe the working of your minds in the act of recollection
more carefully, and you will find something like this. First,
you have a more or less distinct visual picture of the flower,
and then, secondly, a movement-sensation in the nose corre-
sponding to the inhalation of air, and then again, thirdly,
a sensation of touch and temperature, arising from the air
actually inhaled, your movement-sensation having been at-
tended by an actual movement. The sensation of smell proper
is either entirely absent, or, at least, so faint that it is altogether
overshadowed by the other components of the complication.
In the same way the complications consisting in memory-
images of impressions of taste contain hardly anything of the
sensation of taste, which is, however, quite adequately repre-
sented by the movement-sensation, which varies for different
gustatory substances with variation of the accompanying
mimetic expression.

§ HI

Apart from these cases of the confusion of definite sensation-
qualities with muscular and tactual sensations, the separate

Assimilation 287

constituents of a complication are in general clearly dis-
tinguishable, belonging as they do to disparate modalities and
occurring in other connections under other conditions. The
same cannot be said of a second important class of simultaneous
associations, — the connections of an externally excited sense-
perception with its related memory-images. This type of
association we will call assimilation, and speak of the memory-
image as the assimilating element, the sensations following
from the sense-impression as the assimilated. These expres-
sions imply that the memorial constituents are the determining
factors in the result, while the incoming sense-impressions are
determined by them. This is so far true. An impression may
be apprehended in the most different ways, according to the
disposition in which the mind has been left by previous expe-
riences. The resultant complex idea is, therefore, a mixed
product of the impressions given in perception and of an
unknown number of memory-images. But, just because the
idea is a single complex, there can be no question of analysis
into these two constituents. Hence the reproductive elements
are invariably referred to the sense-perception, which now
contains constituents not to be found in the impression which
aroused it. On the other hand, real constituents of the sense-
impression may be wanting in the resultant idea, owing to their
conflict with reproductive elements of greater intensity.

The process of assimilation then, unlike that of complica-
tion, is not one to be discovered by casual introspection. To
examine it, we must carefully compare the impression with the
idea aroused by it. The comparison shows the incongruence
of the two, and so leads us to look for the ground of .their
difference where alone it can be found, — in the activity of
previously experienced ideas. When once our attention has
been called to their influence, we have the key to a whole
number of phenomena of ordinary life and of experimental
practice, which, though striking enough, are generally left
unnoticed or unexplained. We ordinarily read over a printer's
error without seeing it ; that is, we read the familiar word-
picture into the impressions presented to us. Or we fill out
a sentence in a lecture which we have heard indistinctly
without remarking that we have not heard it clearly. On the

288 Lectures on Human and Animal Psychology

other hand, we are equally liable to hear wrongly by supple-
menting the indistinct sounds by a wrong set of memory-ideas.
The crude outlines which serve to represent a landscape in
stage scenery look by artificial light and at the proper distance
to be a perfect reproduction of a real scene. Here the ready
assistance rendered by the appropriate memorial elements is
made still more effective by the confused outlines of the retinal
image. Outline drawings of tridimensional objects, if purely
schematic and unshaded, can be seen at will as tridimensional
or areal, and if the former, as extending in this direction or
in that ; it simply depends upon which of our familiar space-
ideas we employ. For instance, the outline drawing of the
head on a coin can be seen pretty much at pleasure as cameo
or intaglio. You are all familiar with the puzzle pictures
which have, e.g., the head of some well-known man outlined
in the foliage of a tree. At first it is quite difficult to find
the head. But when once you have it, it stays ; and you are
hardly able to get rid of it again, however much you try. The
same thing may often be noticed in stereoscopic observations.
For a time it will be impossible to get the idea of depth, and
then on a sudden it comes with even plastic clearness. What
all these cases mean is, that the assimilating memorial elements
have required some little time to be called into activity by
the appropriate constituents of the external sense-impression.

But, of course, it is not usually a single memory-image which
unites with the given impression in the process of assimilation.
A stereoscopic object which we may never have seen in the
exact form in which it is presented will arouse the co-operation
of a whole number of memorial elements, taken from a whole
number of originally separate perceptions ; and may be able in
this way to call up the idea of three dimensions. But, for this
very reason, it would be wrong to suppose that sense-impressions
are first of all present in assimilation as independently co-
existent ideas, and then fuse to an ideational unity. The assumed
stage of independent co-existence of the components is neither
discoverable by introspection nor actually possible, since, as a
general rule, the assimilating effect proceeds from a large number
of ideational elements, originally distributed through quite dif-
ferent ideational series. We can only imagine that every sense-

4 ssim ilation 289

impression acts as an excitant to numerous tendencies remaining
from previous impressions ; and that such of these as are appro-
priate to the impression, and, at the same time, more easily
excited than the others, help to form the resultant idea. Lastly,
in all these processes of assimilation, which follow directly upon
sense-impressions, the peripherally excited sensations are so far
of influence upon the memorial elements that they increase the
intensity of the reproduced sensations. That is the only possible
explanation of the fact that even in the normal assimilation it
is impossible to distinguish between the ideational elements
aroused by external stimulus and those excited by association.
The impossibility becomes still clearer when the elements of
the latter kind obtain so exclusive a predominance that the
resultant idea is wholly inadequate to the sense-perception.
Assimilations of this class we term illusions. In the illusion, we
imagine that we perceive something which is not there ; that is
to say, we confuse memorial elements with sense-impressions.
And that again is only possible when there is no noticeable dif-
ference in the intensity of the two constituents.

The occurrence of a process of assimilation can be proved with
absolute certainty, as these instances show, when the resultant
assimilation-product is a sense-perception, whether actual or
more or less illusory. In either case the new idea is so different
from the sense-impression that the activity of assimilation is a
matter of direct inference. But you will see that it is at least
extremely probable that assimilations take place in terms of
memory-image pure and simple ; and we have an obvious in-
dication of this in the fact that a particular perception is not as
a rule assimilated by a particular memorial idea, but by an
indefinite number of such ideas. Suppose, then, that there is no
sense- perception present, but that some memory-image crops up
of itself. It will undergo continual variation by assimilating
other ideas which refer to similar objects. So that we cannot
draw any hard and fast line between a memory-image proper
and what is called a fancy-image. Psychologists are accustomed
to define memory-images as ideas which exactly reproduce some
previous perception, and fancy-images as ideas consisting of a
combination of elements taken from a whole number of per-
ceptions. Now memory-images, in the sense of this definition.,

u

290 Lectures on Human and Animal Psychology

simply do not exist. The ordinary memorial representation is
determined by several perceptions of the same object. Thus, if
we try to recall a person whom we have often seen, we never
represent him exactly as he was on any particular occasion ; our
idea of him is the resultant of many perceptions, whose con-
stituents, mutually supplementing or inhibiting one another,
combine partly to deepen, partly to soften, the general outline.
This explains the indefiniteness of most memory-images. Even
when we are recalling an object only once seen, the idea does
not coincide with the original perception ; some elements are
wanting, others which do not belong to the object are wrongly
transferred to it from similar ones. Try, for instance, to draw
from memory some landscape picture which you have only once
seen ; and then compare your copy with the original. You will
expect to find plenty of mistakes and omissions ; but you will
also invariably find that you have put a great deal in which was
not in the original, but which comes from landscape pictures which
you have seen somewhere else. So that, according to the ordinary
definition, every memory-image would be a fancy image, and
ideational reproduction a concept with no corresponding reality.
For there is no memory- image that reproduces either the
primary perception-image, or any other memory-image of that
same perception. And that is not hard to understand when we
remember that our ideas are not permanent objects, but pro-
cesses which can never exactly recur, because the conditions of
their occurrence are never twice alike.

§ IV

The process of assimilation is, therefore, always a compound
process, set up in any particular case by an incalculable number
of elementary connective processes. We may now ask as to the
character of these last, — the indecomposable and fundamental
processes of connection. In answering that question, we must
again set out from those cases of assimilation which begin with
a sense-impression, since they furnish the best material for the
determination of the conditions of the phenomena. There can
be no doubt that there are always two connective processes
running side by side in every case of assimilation, whether this
be normal and initiated by a sense-perception, or illusory and

Theory of Simultaneous Association 291

implying a misinterpretation of sensory impressions. First, the
sense-impression calls up previous similar sensations, and,
secondly, by the mediation of these sensations arouses other
ideational elements not contained in the given impression, but
which were connected with it on other occasions. What first
happens when you look at a stereoscopic object is, that certain
of the outlines correspond to those of some material object known
from previous perceptions. But these coincident elements would
in themselves be wholly inadequate to suggest the actual picture
of a tridimensional object. There must be further aroused
elements not present in the actual figure, but associated in
previous ideas with the coincident parts, and now necessary to
complete the image as that of some definite thing. When we
read a wrongly printed word correctly, the primary suggestion
proceeds from the rightly printed letters in it : they arouse the
corresponding memory-images of the same letters, and these,
again, recall to mind the letters which were visually connected
with them in earlier perceptions, and which, taken together with
them, give the correct picture of the word. So the disturbing
elements in the impression are overlaid by the reproduced ideas.
The older doctrine of association, — i.e., of successive associa-
tion,— distinguished associations as those of similarity and conti-
guity. In the first form an idea is excited which in certain of its
characteristics resembles the exciting idea ; in the second, an
idea which at some time or other was in temporal or spatial
connection with it. If we apply these terms to simultaneous
associations, we may obviously call what was above denominated
the second act in assimilation a contiguity-association. On the
other hand, we cannot reduce the first act in the same way to a
similarity-association. Two objects are similar when certain of
their characteristics correspond, while others are different. Now
it does not seem possible that an impression should directly call
up the memory of another, if this differs from it more or less.
It can, surely, only arouse a memory-image like itself. There
may, of course, follow upon the excitation of these like elements
the reproduction of others which are unlike, provided that these
have been connected with the like in previous ideas. In other
words, a similarity-association always points to the union of a
likeness-association with a contiguity-association. The wrongly

292 Lectures on Human and Animal Psychology

printed word calls up the right image through the likeness-asso-
ciation of the coincident letters, and a contiguity-association,
which takes the right elements, not given in the actual impres-
sion, from previously seen word-pictures. The result of this
compound process is a so-called similarity-association, for the
wrongly printed and rightly ideated words are similar, but not
like. It is just the same with the stereoscopic idea. The out-
lines which originate the suggestion arouse a likeness-association,
which is at once supplemented by one of contiguity, which partly
fills out the resultant idea, and partly corrects it by suppressing
any disturbing elements in the impression. Since no two ideas
are absolutely like, it might be objected that our likeness-asso-
ciation is itself nothing better than a similarity-association. But,
as a matter of fact, we are not concerned here with associations
between complete ideas, but with connections between constitu-
ents of ideas. Absolute likeness between two ideas is impos-
sible, for the very reason that every likeness-association gets at
once attached to it a number of contiguity-associations, the
final result being either a 'similarity' or 'contiguity' association,
according as one or other of the elementary processes predomi-
nates. We cannot discover any other elementary processes than
these two, — the connection of the like and that of the contigu-
ously associated in time and space. Each of them must of
necessity be present in every concrete association. An idea can
only call up an earlier idea, if it has some elements in common
with that ; and since the reproduced idea contains unlike as well
as like constituents, the likeness-connection implies the formation
of a contiguity-connection. Likeness of the elements, you see,
is directly effective. If a new impression contains elements like
those of an earlier impression, these will separate from the rest,
having become so much more familiar by repetition, and will
preponderate in consciousness. Contiguity is only mediately
effective. It works by way of reviving other elements ex-
ternally connected with these like constituents of previously
excited ideas.

In view of this essential difference between the two processes,
is it right to speak of a likeness-connection in the same sense as
a contiguity-connection ? When a given impression arouses an
idea consisting in part of elements belonging to the impression,

Theory of Simultaneous Association 293

in part of elements not actually present in it, but connected with
it in previous perceptions, there can be no doubt that we are
justified in speaking of a connective process in referring to these
unlike constituents ; the corresponding excitations must be set
up by an impulse proceeding from the impression. But the
elements which pass directly from the impression into the assimi-
lation-product hardly seem to need anything which might be
reckoned among the association-processes: they are directly given
by the external sensory stimuli, and would appear rather to be
the condition of the origin of a connective process than its result.
In other words, is not the assimilation-process entirely and
exclusively referable to association by contiguity ?

However tempted we may be at first sight to answer this
question in the affirmative, a little more consideration will con-
vince us that such an answer would be incorrect. As a matter
of fact, the elements which pass from impression into assimila-
tion-product are not in their second connection what they were
in the first ; so that the word 'pass' is only in place if we are
comparing the result with its constituents, and not as referred
to the actual process. The ' passage ' involves the action of
intermediary processes in two different directions. First, the
passage of elements of an impression into the resultant idea is
favoured, as we know from experience, by the frequency with
which they have presented themselves in previous impressions.
The only explanation of that is, that the corresponding excita-
tions are intensified by the dispositions left by the action of
previous impressions. This intensification will, of course, be
directly connected with the present impression ; it will not do
to assume, as those psychologists do who make ideas into per-
manent entities, that constituents of the new idea connect with
constituents of some previous one. It will simply happen that
the greater frequency of certain kinds of excitation implies the
ascription of a higher intensity-value to any one of that kind
which affects us. And it follows from this that the final result
is due not simply to the impression, but, — and this holds of
all association-processes, — to the connection of the impression
with the after-effects of previous excitations. Secondly, this
passage of elements of an impression into the assimilation-pro-
duct implies the presence of another process, the direction of

294 Lectures on Human and Animal Psychology

which is just the opposite of that of the former, — a process of
disappearance of elements which are contained in the impres-
sion, but supplanted in the idea by other new and incompatible
elements called up by contiguity. That is to say, the like ele-
ments are not by any means after the ' passage ' what they were
before it. They are partly intensified by previous practice,
partly weakened or, at least, severed from their original connec-
tions by inhibitory influences. All of which goes to show that
the likeness-connection is as truly the result of many and differ-
ent processes as is the connection by contiguity. At the same
time, we must not forget that these determining processes are
essentially different in the two cases. The best terms to indicate
this difference in brief are perhaps those employed above : the
likeness - connection is immediate, the contiguity - connection
mediate.

LECTURE XX

^ I. SUCCESSIVE ASSOCIATIONS. § II. ASSOCIATION BY SIMILARITY AND
CONTIGUITY ; COGNITION AND RECOGNITION AS SIMPLE FORMS OF
ASSOCIATION. § III. THEORY OF SUCCESSIVE ASSOCIATIONS. § IV.
INDIRECT ASSOCIATION.

§1

IN close connection with assimilation stands, as we saw above,,
the successive association of ideas^ This is the process to
which the general name of ' association ' was originally confined ;
and it is still customary, even at the present day, to speak of
laws of association, and to distinguish in that way connection by
similarity from that by co-existence in space or succession in
time, or sometimes from that by contrast. It is scarcely neces-
sary to say that these are really simply forms, and not laws, of
association ; they are not universally valid conditions of its
origin. They merely serve to furnish classificatory concepts
under which the ready-made products of association can be sub-
sumed. But, curiously enough, the authority of Aristotle and
the constant inclination of the human mind towards logical
schematisation have worked no less harm in this department of
psychology than they worked in the sciences of nature. Aris-
totle had distinguished four kinds of memory, in terms of the
logical opposites ' similarity ' and ' contrast,' ' simultaneity ' and
' succession ' : just as he had arranged the fundamental quali-
ties of all natural bodies under the rubrics of the contraries
4 hot ' and ' cold,' ' moist ' and 4 dry.' And these four forms
have held the field, despite the evidence of observation, down to
our own day. It is now pretty generally agreed that 'contrast'
may be omitted, or, where anything corresponding to it occurs,
referred to 'similarity'; while spatial co-existence and tem-
poral succession are brought under the general head of external

296 Lectures on Human and Animal Psychology

contiguity. This means a reduction of the four forms to two, —
association by similarity and association by contiguity. And
the reduction is so far good that the different cases of successive
connection may, as a rule, be arranged in one or other of the two
classes. At the same time, the terms still tend to suggest the
wrong idea: that they are the distinguishing marks of elementary
processes, instead of the classificatory headings of association-
products, each of which is constituted by a whole number of
simple processes. In the matter of constituents there is, of
course, no essential distinction to be drawn between the two
forms. For it is obvious that just the same processes must be
operative in successive association as in assimilation, — the only
difference between them being that the successively associated
ideas are not combined into one simultaneous idea, but remain
temporally separate, in obedience to conditions which we have
still to discuss.

Apart from this, however, we shall expect to find every suc-
cessive association composed of two processes : a direct connec-
tion of like elements of different ideas, and a connection,
attaching itself immediately to this, of such elements of previous
ideas as have been externally contiguous to those like constitu-
ents. If, as we look at the total result, the connections of the
like elements are predominant, we speak of a similarity-associa-
tion ; if the external connections are the stronger, of a contigu-
ity-association. Thus it is an association by similarity when the
picture of a landscape reminds us of the reality as we have actu-
ally looked upon it. Different as the picture and the retinal
image may actually be, there are certain outlines that corre-
spond. These call up the memory-images of earlier perceptions,
and cause us to transfer to the picture many of the elements of
the original which it does not really possess. Now this revival
of elements which are not given in the picture is plainly an
association by contiguity. Certain of these contiguity-elements
work by way of assimilation ; they make the similarity of the
picture to the original appear greater than it is. Others make
against assimilation ; it is through these that we are able to dis-
tinguish picture and reality at all, — that the result of the whole
process is not a simultaneous assimilation, but a successive simi-
larity-association. On the other hand, if we have read the

Association by Similarity and Contiguity 297

letters a b c d, we are inclined to continue e f g h. This is
a case of association by contiguity. But here, too, the original
process is the direct connection of like with like. The letters
when read call up the like letters previously read or heard.
And it is at this stage that contiguity-effects must intervene, if
the visual idea is to be apprehended as agreeing with previous
perceptions. Then, by a further operation of contiguity, the
absent letters are supplied to complete the usual series.

Association by similarity and association by contiguity, then,
differ in two points as regards the nature of their constituent
processes. First, there is a general predominance of the ele-
mentary connection by likeness in the former, of that by con-
tiguity in the latter, form ; secondly, in the similarity-associa-
tion our attention is directed upon the common properties of the
ideas, in the contiguity-association upon their divergences. The
association of the picture with the landscape is an association by
similarity, because the resemblance of the two ideas makes us
neglect not only their differences, but also contiguity-connec-
tions which are essential for the institution of a comparison.
The association of the letters of the alphabet is an association
by contiguity, because we attend only to the added letters, and
not to the cognition of the first letters and the likeness-connec-
tions which it almost invariably involves.

§ II

The result of all this is, that there are two fundamental forms
of connection between ideational elements : connection by like-
ness and connection by contiguity ; and that both of them are
concerned in every case of actual association. For the proof of
this fact our best recourse will be to the simplest cases of asso-
ciation. They possess the further advantage of exhibiting with
especial clearness the conditions which differentiate successive
from simultaneous association, and particularly from assimila-
tion. The constituent elementary processes are, of course, the
same in both forms.

The simplest case of assimilation is the cognition of an object ;
the simplest case of successive association, its recognition. We
cognise a picture as a picture even when we are perfectly sure
that we have never seen it before ; we recognise it in remember-

298 Lectiires on Human and Animal Psychology

ing that we have seen it, just this particular picture, on some
previous occasion. The simple act of cognition is a process of
assimilation. The present impression calls up earlier ideas :
there are set up connections by likeness and contiguity, but there
is no analysis into a succession of ideas ; the presented and the
memorial elements combine at once to a single idea, referred to
the actual impression. The fact that the resultant idea is, how-
ever, no new one, but one which, upon the whole, is familiar,
expresses itself in the character of the accompanying feeling.
We will call this the feeling of cognition. Since feelings always
have some ideational basis, we may suppose that the indefinite
memory-images in the background of consciousness, whose func-
tion is the assimilating of the given impression, serve as the
intellectual substrate of this particular feeling.

From this process of cognition is developed that of recogni-
tion. The steps are three in number.

Most closely related to the act of cognition is the process of
immediate recognition. In this we are either unconscious or but
obscurely conscious of the connecting links by whose aid recog-
nition is effected. And here again two alternatives are possible :
first, the idea is merely accompanied by the consciousness that
it has been before our minds before, at some time or other, once
or oftener, — that is, the recognition takes place without there
being any recollection of attendant circumstances. Secondly,
though the recognition is immediate, it involves the recollection
of attendant circumstances. We recall the temporal relations
and spatial surroundings in which we previously made the
acquaintance of the recognised object. In both cases the act of
recognition is accompanied by a feeling. Where the first form
of the process occurs, this is generally indefinite, and may be
connected with the emotion of doubt. But it becomes distinct
and vivid as soon as there is conscious localisation of the recog-
nised idea in time and space. We may call this feeling the feel-
ing of recognition. Now the recollection of attendant circum-
stances consists merely in the excitation of secondary ideas
externally contiguous with the recognised object in previous
experiences. In other words, the act of recognition requires
these contiguity-connections for its completion.

The second form of immediate recognition furnishes the tran-

Association by Similarity and Contiguity 299.

sition to a third form of the general process, — to mediate recog-
nition. In this we are clearly conscious from the outset that
recognition is brought about by the mediation of secondary
ideas. Think how often you meet a person whom at first sight
you take to be an absolute stranger. But he tells you his name,
and on a sudden the face that was so unfamiliar shows you the
features of an old acquaintance. Or there may be other mediat-
ing circumstances. You see a third person whom you have
often noticed in his company, and your eyes chance to fall on a,
coat or a travelling-bag that awaken your memory. Here again
there is a special feeling regularly associated with the act of
recognition. This feeling comes later and arises more gradually
than the immediate recognition-feeling. At the same time, you
will find that it may be very vivid, even when the apprehension*
of the agreement between the present idea and a previous one is-
still quite indefinite.

There can be no doubt that instances of mediate recognition,
(in this sense) occur which are wrongly taken for cases of imme-
diate recognition, the reason being that we are not clearly
enough conscious of the auxiliary ideas which mediate the
recognition. Thus it has been shown by experiment that it is
quite easy to hold in mind three shades of grey between the
extremes of black and white, and to recognise each of them cor-
rectly, and apparently immediately, after the lapse of some time ;.
while, if one more shade is interposed, their recognition is un-
certain, and mistakes are many. Now there are in common use
in language just three designations of shades of grey, — dark grey,,
grey, bright grey. So that it is not hard to see a reason for
the definite limitation of recognition. We have only to assume
that one of these three verbal ideas was involuntarily associated
with each of the three impressions, and that it mediated the
recognition. A musical ear can recognise a particular musical
clang after a long time, if this possesses a definite tonal quality,
and has its definite place in the musical scale marked by some
note-name. But recognition becomes impossible very soon after
the giving of the impression, if some other tone is taken which
cannot be definitely associated with a name like c, c$, dt etc.

We have seen that these different forms of recognition pass
over into one another by degrees. It might appear doubtful

300 Lectures on Human and Animal Psychology

whether they should be regarded as different processes at all,
and not rather as modifications of one and the same process,
differing only as regards their secondary conditions, i.e., in the
•clearness or temporal course of the various conscious elements.
Thus mediate recognition, and immediate recognition with attend-
ant circumstances obviously differ only in this, — that while in
the former the secondary ideas are first apperceived, and there
then arises the consciousness of the agreement of the principal
idea with that experienced before, in the latter these secondary
ideas are only clearly apprehended at the same time with the
agreement of the two principals, and maybe even later. Now,
the apperception of an idea is not the same thing as its appear-
ance in consciousness. Our discussion of the phenomena of time-
displacement (pp. 270, 271) showed us that when two ideas, a and
•b, follow each other in rapid succession, the second, b, may be
apperceived before the first, a, which certainly anticipated it in
consciousness. It is possible, i.e., that an apparently immediate
recognition with secondary ideas is in reality a mediate recogni-
tion as well. The secondary ideas might exert just the same
influence in this latter case, although they were longer in coming
to clear consciousness. The difference between the two forms
will then depend essentially upon the rapidity with which the
ieeling of recognition arises. If it is excited by the bare
entrance of the secondary ideas into consciousness, we call the
recognition immediate. If there are required a longer operation
and a greater degree of clearness of the secondary ideas, the act
of recognition becomes mediate.

Now, if the difference between these two forms reduces itself
to a difference of degree in the efficacy of the secondary ideas, it
is plain that there can be no sufficient reason for regarding simple
recognition without attendant circumstances as a process sui
.generis. If the secondary ideas, the whole scope of whose acti-
vity is that of auxiliary forces, may in cases be raised to clear
-consciousness only after the recognition has taken place, it will
surely be possible that they may entirely disappear from con-
.-sciousness as soon as the result of that recognition begins to

o o

take effect. As a matter of fact, a closer glance at the condi-
tions serves to make the possibility a probability. Immediate
recognition occurs, first, where the objects are completely fami-

Association by Similarity and Contiguity 301

liar to us from repeated experiences, and, secondly, where we
have come to know them but a short while before, or under
circumstances in which they made an especially deep impression
upon our feelings. Now these are conditions which render in-
telligible a quick apperception of the object, with an accompany-
ing feeling of recognition, but which by no means indicate as
probable the absence of the otherwise universally present second-
ary ideas. When we see a person with whom we are daily
associating, there are so many reproductions of the most various
situations in which we were in his company, that it is very diffi-
cult for any particular one among them to come to clear con-
sciousness. But at the same time there may always be operative
a certain number of these obscure secondary ideas, which will
explain the presence and vividness of the feeling of recognition.
It is a little different when we see some one for the second time
whom we met but a short time before. The recognition-feeling-

o o

in this case is certainly not without its foundation in attendant
secondary ideas. But these are fewer in number, and not in
opposition to one another. They therefore possess a more defi-
nite character, and so are, as a rule, easily perceived, if the atten-
tion is directed upon them. In other words, the process in this
instance appears to assume the character of an immediate recog-
nition, for the sole reason that the connection of the secondary
ideas with the object is still so close, that no perceptible time is
required for the excitation of the recognition-feeling.

It would seem, then, as though the feeling of recognition, —
which, as introspection shows, takes on very different shades in
the different cases we have been discussing, — depended in every
instance upon the excitation of auxiliary ideas. But the time
which these secondary ideas take to appear is not always the
same ; and that points to another difference between the process
of assimilation and the act of recognition. If a given impression
calls up an earlier idea without exciting secondary ideas,
whether clear or obscure, and without reviving the feeling which
is dependent upon them, the result is an assimilation. Impres-
sion and idea are combined to form a simultaneous whole ; the
conditions of recognition are wanting. We perceive the object
as one of a class with which we are familiar without referring it
to anything definite of which we have had previous experience.

.302 Lectures on Human and Animal Psychology

And it is for this reason that we speak of an act of cognition
rather than of recognition. In other words, we may oppose the
-act of recognition in general, as a simple case of successive
association, to the act of cognition, which is a simultaneous
association.

We have already seen that contiguity-connections are involved
even in the act of cognition. We should not be able to bring
our visual idea of an object under the head of a familiar class, if
the likeness-connections which arise first did not immediately
call up contiguity-connections from earlier perceptions. But
since these last remain wholly indefinite, — they may possibly be-
long to quite different and unrelated ideas, — the result is only a
feeling of cognition : the object is regarded as a new presenta-
tion, but one belonging to a class of known ideas. So that,
-although the recognition-feeling is certainly akin to the cognition-
feeling, there is a greater qualitative difference between these
two than exists between the different shades of the recognition-
feeling mentioned above. And the feelings are not only differ-
ent in quality, as is to be expected when we consider the
different conditions under which they appear, but also in inten-
sity ; the feeling of recognition is generally far more intensive.
Parallel with these differences, again, run differences in time-
relations : the recognition-feeling comes later, and its gradual
intensification can usually be clearly followed in introspection ;
while the cognition-feeling generally seems to appear simul-
taneously with the impression. These are differences which are
at once explicable when we remember the different nature of the
underlying association-processes.

The two feelings correspond most nearly in all their attributes
in the case of simple recognition of persons or objects familiar
to our every-day experience. Here the total process of recog-
nition is very closely related to that of assimilation. On the
other hand, the feeling of recognition is most characteristically
itself in the case of mediate recognition.

There can be no doubt whatever, in the case of mediate re-
cognition, that the secondary ideas upon which the recognition-
feeling depends are actually present in consciousness. Indeed,
we are in this process not only conscious of the presence of the
secondary ideas : we see quite clearly that the attendant feeling

Association by Similarity and Contiguity 303

is bound up with them. But what shall we say of immediate
recognition, when these auxiliary ideas are either not noticeable
at all, or are only found by introspection after the act has taken
place ? We may assume either that they are below the limen
of consciousness, and rise above it, if i\t all, only at a later stage ;
or that they are in consciousness throughout, but in so obscure
a fashion as not to be perceived at first. The experiments
made upon the different degrees of clearness of ideas with
momentary transitory impressions, which we have already re-
ferred to (pp. 241 ff.), declare for the latter hypothesis ; it can
hardly be doubted that the auxiliary ideas are in consciousness,
however dimly and obscurely. The different ways in which
those experiments showed us that obscure ideas could make
their presence known in consciousness correspond exactly to
the various phenomena of immediate recognition. Sometimes it
is possible, after the completion of the act, to represent its
circumstances in detail ; sometimes there is left only the in-
definite feeling that the object was seen. So that the not
infrequent impossibility of localising the recognised object in
space and time is no proof at all against the presence of obscure
auxiliary ideas. On the other hand, it is at least a very im-
probable supposition that ideas which have disappeared from
consciousness can nevertheless exert an influence upon it in the
form of a definite feeling. For if an idea that has disappeared
can still excite a feeling in consciousness, it must possess posi-
tive attributes in its unconscious condition which completely
resemble those attaching to it as a conscious process. The
recognition-feeling, you see, is essentially the same whether the
recognition is immediate or mediate, i.e., mediated by clearly
conscious secondary ideas. That supposition, in other words,
would plainly commit us to the adoption of the untenable
position that ideas which have disappeared from consciousness
still persist in an unconscious condition, possessed of the same
attributes as attached to them in consciousness : or, to put it a
little differently, the vanished ideas would be indestructible
objects, and not those dispositions towards the repetition of
previous processes which the facts tell us they really are.

304 Lectures on Human and Animal Psychology

§ HI

The process of recognition was described above in general
terms as a simple form of successive association. To this must
now be added that its various forms present a continuous
serial transition from simultaneous to successive association.
Immediate recognition, which approximates most nearly to the
simple act of cognition, comes in all respects very near that of
assimilation. The only indication of an ideational basis lying
outside the recognised object is the characteristic feeling of
recognition, which even here usually requires a certain time to
arise. If these extraneous ideas come subsequently to clear
consciousness, the simultaneous association passes over of its
own accord into one of succession. And just the same may
take place with the act of cognition. When an object has been
assimilated by previous ideas of the same kind, one of two
things may happen : certain particular secondary ideas, con-
tiguous with the assimilating ideas, may enter into consciousness,
or from the whole number of assimilating ideas there may be
singled out particular ones, which subsequently attain to a
greater clearness.

If in a series like this an associatively excited idea is appre-
hended as having been previously experienced in its own special
quality, the process becomes a successive act of memory. Such
a memorial act results directly from the different forms of cog-
nition and recognition when the ideational acts which are in
them given simultaneously or almost simultaneously are divided
up into a clearly conscious temporal series. And just in these
transition-cases we may perceive with especial clearness the
condition of such a temporal analysis. This condition is given
in the fact that the separate constituents of a total associative
complex require periods of various duration to attain to clear
consciousness. In immediate recognition and in the simple act
of cognition there is no clearly noticeable succession, because no
sooner is the impression given than the elements of the assimi-
lating ideas which cohere with it are also apprehended. But
even in mediate recognition there is not only a distinction
between the secondary ideas and the principal impression, but a
temporal dissociation of them in introspection : the secondary

Theory of Successive Associations 305

ideas come first. This time-relation may vary further in the
most diverse ways. The principal idea may be assimilated first,
the secondary ideas coming later as revivals of earlier experiences;
that is a case of ' association by contiguity.' Or an assimilation-
process of the usual form, involving an indefinite number of
assimilating ideas, may run its course, and then certain of
these ideas be held in consciousness by themselves ; that is ani
ordinary ' association by similarity.' If this consists in an act
of recognition of the kind described above, and if there are
further associated with that other secondary ideas previously
contiguous with the cognised object in space and time, the pro-
cess is one of recollection.

The analysis of associations into temporal series depends in
all these instances upon two conditions. First, one of two re-
vived ideas may enter consciousness later than the other. This
is realised in the case of mediate recognition, and in the simple
memorial processes developed from it. Secondly, while several
revived ideas may appear simultaneously in consciousness, and
perhaps exert each its own influence upon the state of feeling, they
may nevertheless be successively apperceived, coming one after
the other to the conscious fixation-point. This is, of course, the
case in all acts of recognition with temporal and spatial locali-
sation. At the same time, this condition is probably quite often
crossed by the other ; it is in consequence of this temporal and
spatial localisation that individual ideas become conscious at
all.

The result of these paragraphs is to show that the connections
operative in successive associations are the same as those which
constitute simultaneous associations. The first thing always is,
that certain elements of our ideas call up the like elements of
other ideas. To these attach others which at some time or
another were connected with them. And the whole process is
perpetually shaped and modified by two influences, — the mutual
intensification of the like and the mutual repression of the
opposing elements. So that all our mental experiences are con-
tinuous and interconnected ; the sum of ideational elements
which consciousness has at its disposal forms an unbroken,
interlaced and intertwined whole, within which each separate
point can be excited from any other point by the mediation ot

X

306 Lectures on Human and Animal Psychology

those lying between them. Every idea which comes into
consciousness, so far as it is not the direct product of sense-
impressions, is the result of associative operations initiated in
this continuous interlacement of ideational dispositions. And
the sense-excitations themselves, as the phenomena of assimila-
tion and complication show us, everywhere connect with
elements which belong to this network of association. So that
the ideas of memory and imagination differ from the direct
perceptions of sense only in the degree, not in the manner, in
which they arouse the associative activity.

§ IV

But may there not appear in consciousness ideas due neither
to sense-impressions nor to association ? Is it not a matter of
frequent occurrence enough that some fancy-image comes up in
our minds for no known reason, and with no discoverable refer-
ence to any directly preceding experience ?

Cases like that have led to the assumption of a spontaneous
origin of ideas. The apparently unmediated idea, it is said, had
been inhibited by others ; and as soon as these were in their
turn inhibited by yet other ideas, it rose of its own accord into
consciousness. These inhibitory processes are, of course, entirely
'hypothetical. No one has perceived them, or even any definite
facts which would allow us to infer their existence. Moreover, it
is clear that this explanation of the ' spontaneous origin ' assumes
once more the imperishability of ideas, or at least their persist-
ence in an unconscious state, in which they possess exactly
the same attributes as attach to them in consciousness, except-
ing the property of being conscious. Of this they are tempo-
rarily deprived by their ideational enemies. Such an assumption
is untenable ; the ideas, as we have urged so often, must not be
regarded as unalterable objects, but only as varying processes.
Experiment gives us the key to the difficulty. The phenomena
of indirect association, which are very easily demonstrated,
explain at once the apparently ' spontaneous ' origin of ideas.
We can reduce the whole matter to terms of association.

An observer is stationed in a dark room, or looks into a dark
chamber. Momentary light-stimuli are presented to him in
regular succession. First of all, the series consists, say, of the

Indirect Association 307

objects a, b, c, d, e, f. . . . In a second and immediately
following experimental series, each of these objects is connected
with another, and in such a way that certain members of the
series have attached to them the same secondary ideas ; e.g., a a,
/>/?, c 7, d S, e a, f 7, g ft. . . . After some time the principal
terms of the series, a, b, c, . . . are presented again in a
different order, and without the secondary objects a, ft, 7. . . :
e.g., f, b, a, g, e. . . . If sufficient time is allowed after each
impression for the formation of an association, it is found that in
a relatively large number of cases there are associated ideas
from the same series, which were connected with identical
secondary ideas ; e.g., e will be associated to a, g to b, etc. This
result is most striking when the principal ideas, a, by c, d. . . . are
familiar objects (a house, a tree, etc.), and the secondary ideas,
<*. & 7, S. ... arbitrary signs (e.g., letters from a language with
which the observer is unfamiliar). In this case the secondary
ideas which are such effective aids to association are but seldom
clearly remembered. And so the observer, when he is asked
why he associates the definite idea e to another, a, replies that
he cannot tell. If you recall what we have said above as to the
efficacy of such secondary ideas in the acts of cognition and
recognition, you will see that we must assume in this present case
that the secondary idea a was obscurely present in conscious-
ness and excited e, with which it had previously been connected,
whereupon e, which had frequency and familiarity in its favour,
appeared by itself in the foreground of consciousness. That is,
the only difference between this process and an ordinary associa-
tion is, that here certain members of the associative series remain
unknown, with the result that the connection appears to be
broken at the places where it is mediated by them. Occasions
to this indirect form of association cannot be rare. We shall,
therefore, be justified in always referring to it purporting in-
stances of the spontaneous origin of ideas in consciousness,
although, from the nature of the case, it is only exceptionally
that we can prove the efficacy of the unapperceived middle
*erms.

LECTURE XXI

§ I. CONCEPTS AND JUDGMENTS. § II. DISTINGUISHING MARKS OF
INTELLECTUAL PROCESSES. § III. DEVELOPMENT OF THE INTEL-
LECTUAL FUNCTIONS. § IV. MENTAL DERANGEMENT

§ *
A SSOCIATIONS are due to the interconnections obtaining

within the whole circle of our ideational consciousness.

And it is a necessary corollary from this that all the
relations into which ideas can enter with one another take their
origin from those connections by likeness and contiguity which
lie at the root of the association-process in general. But it is
equally plain that the inference so often drawn, ' all ideational
connections are associations,' is wholly unjustifiable. This infer-
ence has its source in an error with which we are already familiar,
— that which transformed the forms of association into ' laws of
association.' It rests upon the supposition that these forms are
themselves elementary processes, whereas they are really, as
we have seen, complex products resulting from the elementary
connections by likeness and contiguity. But while we grant
that all the possible interrelations of ideas are reducible to
these two elementary types, we do not mean to assert that the
association-products can be exhaustively and without exception
classified under the heads of simultaneous and successive associa-
tion. There is one limitation which must not be disregarded.
We never speak of association except where the elements
which mediate the connection belong to a restricted circle of
ideas. Thus assimilation is confined to perceptions of so homo-
geneous a character that they can be connected to form one
single idea, complication to disparate impressions, which are
inseparable concomitants in perception. The same thing holds
of successive associations by similarity and contiguity, which,

you remember, only differ from simultaneous associations in the

308

Concepts and Judgments 309

(specially conditioned) temporal separation of the individual acts
of ideation.

Now there can be no question that we find processes in con-
sciousness which are inexplicable in terms of these associations
between similar or frequently connected perceptions, although,
certainly presupposing the existence of the association-products
Let us consider for a moment one particular class of ideas,
which is of all the processes of the same generic kind that which
most resembles association as regards conditions of origin, but
which nevertheless is quite characteristically different from it. I
mean the ideas which we call concepts. If our eye lights sud-
denly upon the picture of a man, the first thing that occurs is an
effect of assimilation : we cognise the picture as that of a man
in virtue of its likeness- and contiguity-relations to previous
perceptions. If these relations are of so individual a nature,
that they suggest a similarity-association with some definite
person, the originally indefinite act of cognition passes over into
an act of recognition. There may then further attach to this
a number of successive contiguity-associations ; we remember,
it may be, the circumstances in which we saw the recognised face
for the last time, or upon some special occasion, and so on. All
these processes arise under obvious associational conditions ;
but not one of them gives us the concept of man. It is, indeed,
perfectly true that if the concept happens to be a very familiar
one it may be more or less clearly present in the association.
In the nature of the case, however, that is not necessary : the
simple cognition of an object as known does not in any way
imply a concept, although simple acts of cognition and recog-
nition must inevitably precede the formation of concepts in
general. How, then, do we distinguish a concept from an
ordinary idea, which is cognised as agreeing with some other or
with several others ? It is obvious that the conceptual quality
cannot be a specific attribute of the idea which stands for the
concept in consciousness. There is nothing in this, considered
apart from its relations, to distinguish it in any way from any
other particular idea. No ! the only distinguishing mark of the
conceptual idea consists in the accompanying consciousness that
the particular individual idea has only a vicarious value, and
that therefore any other particular idea which belonged under

310 Lectures on Human and Animal Psychology

the same concept, or was in any way to be thought of as an
arbitrary sign of it, might be just as well put in its place. This
accompanying consciousness is also attended by a characteristic
feeling, a conceptual feeling, which is wholly different from the
feelings of cognition and recognition, and points to a divergent
ideational substrate. And this feeling, again, can only consist
in concomitant ideational processes, running their course very
likely in the more obscure regions of consciousness. In the
present case, these processes must evidently be those which give
to the concept-idea the peculiarities distinguishing it from other
ideas. Processes of this kind are processes of judgment, as
may be seen from the fact that concepts do not exist from the
first in isolation, but obtain their conceptual significance only as
elements in judgment. Whenever, therefore, we think of the
concept in isolation, we are thinking of it as a constituent of an
indefinite number of judgments ; no other case is possible. In
this instance, then, the secondary ideas will be obscurely con-
scious judgments, in which the concept occurs ; and they will
tend in particular to be judgments which somehow contribute
to a definition. If, e.g., we think of the concept ' man ' in isola-
tion, we have before us at the fixation-point of consciousness
either the image of some individual man, or the word ' man ' (as
vicarious sign), or perhaps a complication of the optic and
acoustic images. In its more obscure and outlying regions,
and probably moving restlessly from this part to that, are a
number of judgments in which the concept is involved, and of
which only an occasional one may rise here and there to clearer
ideation. But, obscure as they may be, they serve to invest the
concept-idea with the consciousness of its vicarious significance,
and with the resultant concept-feeling. You see, this signifi-
cance and the feeling which accompanies it attach to the
immediate introspective perception that in all these judgments
the idea might have been a different one.

Now we have already seen that acts of cognition and recogni-
tion are also attended by secondary ideas, which on the one
hand give rise to the peculiar feelings accompanying these
processes, and on the other, if they happen to come clearly
before consciousness, arrange themselves to a temporal series of
interconnected ideas. But if cognition, recognition, and

Concepts and Judgments 3 1 1

concept are so far alike, it is just at this point that we are able
also to lay our finger upon the essential difference between
the first two processes and the third. This temporal series is
always a similarity- or contiguity-association, in which (as the
name implies) each idea persists as an independent unity. For
objects which resemble one another, or which are contiguous in
space and time, may certainly be combined to form more com-
plex ideas ; but every part of the resulting compound process
is still independent, so that if it becomes dissociated from its
companions, it continues unimpaired in consciousness. But with
concept-ideas, as with all conscious content which belongs to
a logically coherent thought-process, the case is very different.
The significance of the individual is now entirely dependent
upon the whole of which it forms a part. Dissociated from
this, it no longer possesses any significance of its own. Or if
it seems to, the explanation is the same as for the concepts
which we think of in isolation ; we can confer a significance
upon it in so far as, for this special purpose, we leave the
logical connection in which it belongs undetermined. Thus the
concept ' man,' when we think of it without reference to any
context of judgment, can only have this significance: that it
may be subject or predicate of a large number of judgments.
Only as such an indefinite element of a logical thought is it a
' concept ' at all. In all other cases the corresponding idea
would be simply and solely a concrete particular idea.

An objection might be raised to this train of argument. ' It
may be quite true,' you will say, ' that concepts and their con-
nections are in many respects different from ordinary associa-
tions arising between particular ideas. But that is no reason
for refusing to reduce them, and all logical thought-processes
with them, to associations in the wider sense, perhaps associa-
tions of a peculiar and more complex nature.' The objection
does not hold. The differences between the two kinds of
conscious process are characteristic and fundamental, as evident
to subjective perception as they are manifest in the uniformities
objectively discoverable. To employ one name for both, and
so to suggest the view that the processes are of the same kind,
would serve not to clear, but seriously to embarrass, the path of
investigation.

3 1 2 Lectures on Human and Animal Psychology

§ II

The most obvious subjective mark of the intellectual conscious
process, as distinguished from association, is the accompanying
feeling of activity. The very best means of arousing a purely
associative, — i.e., not logical, — train of ideas is to assume the
most passive attitude possible, to repress that activity of
thought which requires volition to initiate it, and is attended by
the activity-feeling. The question what this activity is, and in
what the feeling of activity consists, has been already answered
in our discussion of voluntary action (Lecture XV.). In virtue
of its subjective characteristics, intellectual activity falls at once
under the concept of internal voluntary action, or active appercep-
tion. In this sense, then, we may distinguish intellectual pro-
cesses from associations, on the purely psychological basis, as
apperceptive connections of ideas. By a 'free' or 'voluntary'
action, we do not, of course, here, any more than in our previous
discussion, understand an unconditioned action. The phrase
simply means that changes in consciousness are involved
which are not explicable by reference to individual ideational
connections, but only as resulting from the general tendency
of all our conscious content at any given time, — in the last
resort, that is, from the whole of the previous development of
consciousness. If we term the result of this total development
our ' self,' we must regard this self as the cause of all in-
tellectual processes.

These considerations make it self-evident that the range of
the subjective relations to which these internal processes owe
their origin may vary enormously. No excitation, of course,
•can affect at once the whole number of our acquired disposi-
tions. For the action to take rank as a voluntary intellectual
activity, it is only necessary that groups of ideas be impli-
cated which do not stand in any obvious associational relation
to those directly preceding them. And, in the same way, it is
inevitable that associations intrude upon the intellectual
functions. And with reference to this it is especially signifi-
cant that the intellectual ideational connections, once formed,
themselves enter into contiguity-relations, and can therefore be
revived in the form of external association. In this case, of

Distinguishing Marks of Intellectual Processes 313

course, there is no trace of the feeling of activity which else-
where accompanies the intellectual processes. Such a transition
from apperceptive trains of thought to association is of the very
greatest importance : it facilitates constructive mental work in
a high degree. In this sense it forms one of the principal
constituents of those various practice-processes which gradually
enable us to perform voluntary actions, at first matters of
intention and reflection, as appropriate mechanical reactions to
definite external stimuli. So universal is it, that for the
accomplishment of external acts of will the interposition of a
voluntary decision is only necessary at certain critical moments ;
their detailed execution is relegated to the mechanism which
practice has perfected. And, in the same way, the active work
of thought in the intellectual processes becomes more and
more confined to the essential moments in the flow of thought,
while our thinking on all subordinate points goes on with no
other aid than that of logical associations. The more practised
in thinking we are, the more numerous become the middle
terms which suggest themselves, and the more real force and
energy has thought to bestow upon decisive issues.

With these subjective characteristics are united not less im-
portant objective peculiarities, distinguishing the intellectual
processes from associations. They are given in the totally
different character of the temporal succession in the two cases.
In successive association one idea follows on the other as the
various likeness- and contiguity-connections operative in the
case determine. Each particular idea retains its independence.
And since in a long associational series a new idea is regularly
associated with only one of its predecessors, generally the most
immediate, the series is subject to abrupt changes of the most
varied character. Beginning and end in particular may be
wholly unrelated, however complete the chain that connects
term with following term. In contradistinction to this, the
intellectual processes always begin with aggregate ideas. These
differ from the complex ideas resulting from simultaneous
association in that they do not consist of connections which
(like position in time and space) appear as direct objective
attributes of the idea ; but the relations existing among their
•constituents are regarded as conceptual determinations, into

314 Lectures on Human and Animal Psychology

which the complex object is analysed by the activity of
thought The basis of such an aggregate idea, however, is
always a complex idea associatively produced. Thus the im-
pression of a red house gives rise, by means of associative fusions
and assimilations, to a complex visual idea. This only becomes
an aggregate idea when the red colour is separated from the idea
of the house as such. For then attribute and object are con-
ceptually thought, and brought into mutual relation in the
aggregate idea.

§ HI

The first products of intellectual activity, then, are simul-
taneous aggregate ideas. Their only difference from ordinary,,
associatively formed ideas consists in this, — that the ideated
object is regarded as analysable in terms of arbitrarily selected
thought-relations. As soon as one or more such analyses have
been carried out, their simultaneous connection gives rise to a
train of thought. This process is best seen in the acts of logical
thought in the narrower sense ; i.e., in the processes of judgment
which are expressed in language. These are completely
different, even in outward form, from the associative series.
In the latter one idea joins on to another indeterminately ; but
logical thought is governed by a dichotomic law, admitting of •
no exception, except when associations intrude upon the apper-
ceptive train of ideas in the manner specified above. The
clearest expression of this law is to be found in the grammatical
distinction of the parts of the sentence. The division is either
simple, as in the simple sentence, where subject and predicate
each consist of one single idea ; or it is multiple, as in all kinds
of compound sentences, where each of the principal constituents
can again be subdivided on the same plan, the subject into
substantive and adjective, the predicate into verb and object,
verb and adverb, etc.

But this external law or uniformity is the result of internal
conditions. Thought is always a discriminating and relating
activity. That its analysis follows the above rule is due to the
fact that it separates the constituents of an aggregate idea only
to bring them at once into some mutual relation, — a relation
determined after the comparison of numerous ideas, partly

Development of the Intellectual Functions 3 1 5

alike and partly different. The aggregate idea of the red house
and the resultant judgment, ' the house is red,' can plainly not
arise until many ideas of houses have been formed, with vary-
ing colour-attributes. Then, and then only, will it be possible
in a particular case either to abstract the attribute from the
object of experience, or to refer it to an object thought as exist-
ing independently of it

It might perhaps be objected to this discrimination of the
aggregate idea from the judgment that when once we have
separated the former from the ordinary complex idea we have
ipso facto constituted it a judgment. It is impossible, e.g., to
think of an object as logically connected with any of its
attributes without this connection finding immediate expression
in a judgment. But certain as it is that the simplest judg-
ments (like ' the house is red ') can hardly be distinguished
in fact from their corresponding aggregate ideas (' red house ')r
the possible confusion ceases with them. For consider those acts
of thought which presuppose a continued process of subdivision.
When we are about to express a complicated thought, what is-
first of all in consciousness is the total thought in the form of
an aggregate idea. But it is quite impossible to say of this that
it is identical with the judgments into which it is analysable.
No ! we can perceive well enough that while the whole thought
is already there as an aggregate idea before its expression, its
separate constituents are only raised to clear consciousness in
proportion as their analysis is actually carried out. Aggregate
ideas are, therefore, the more indefinite the more comprehensive
they are, the more numerous the acts of judgment they require
for their complete determination.

We must, however, remember that the logical judgment is
not the only, — more than that, it is not the original, — form
which apperceptive ideational processes take in consciousness.
The commonest case is, that aggregate ideas of a more or less
comprehensive character are consciously analysed in the form
of sense-perceptions. The unitary character of the complex
process means even here that each act of division within an-
aggregate idea (provided that this has been held in mind for any
considerable time) attaches closely to its neighbours. But the
purely perceptual nature of the contents and the absence of any

316 Lectures on Human and Animal Psychology

formulation of it in logical terms lead to the replacing of the
dichotomic law by the general impression of an analytic process,
which runs its course in orderly sequence, and sets out from a
single aggregate idea. To this must be added that it is a more
obvious fact in such instances than it is in conceptual logical
thought that ideational analysis implies an ideational explication.
The products of analysis, at first but obscurely apprehended,
oftentimes fail to obtain a more clear and distinct content until
they have entered into new associations. This perceptual form
of intellectual elaboration is the activity of imagination. In other
words, imagination is in reality a thinking in particular sense-
ideas. As such it is the source of all logical or conceptual
thought. But it continues to exist alongside and independently
of the latter both in the unguided play of fancy of our every-day
life, and in the finished creations of the artistic imagination.

§ IV

To give a complete account of the intellectual functions
would extend beyond the limits of our present undertaking.
Part of that account, — the description of the conceptual or
logical forms of thought, — lies within the province of logic ;
part of it, — the consideration of imagination as a form of
intellectual activity, — within that of aesthetics. But it is of
psychological interest, and desirable for the right understanding
of the relation of association to intelligence, that we should
pause here to cast a glance at the alterations produced in the
train of ideas and the mental processes to which it gives ex-
pression by the different forms of mental derangement.

The most clearly marked and most permanent of these
•derangements are the various kinds of insanity. The particular
forms of insanity, as you know, are so many and so different,
that pathological psychology has as good a claim to rank as
an independent discipline, beside normal psychology, as has
the pathology of the body to be separated from its physiology.
This latter separation was long ago effected ; the two disciplines
are independent sciences, quite apart from the fact that patho-
logy has also practical applications. Add to this that
•every mental derangement involves, besides alterations of the
intellectual processes and associations, other and equally

Mental Derangement 317

fundamental modifications of the mental life: especially de-
rangements of sense-perception and of the emotions, as
compared with which the ideational disturbances often appear
as merely secondary consequences, though it is true, — and you
will understand it when you consider the inextricable inter-
dependencies of all these mental processes, — that these altera-
tions of ideational content will react again upon the affective
and conative side of consciousness. Here, however, we shall
leave all this out of account, and simply look at mental de-
rangement from the single point of view of alteration in the train
of ideas. And in this respect we shall find it in its funda-
mental character, despite differences of detail, uniform and
homogeneous throughout.

This much may, however, be said with regard to the altera-
tions produced by mental derangement in the spheres of sensation
and emotion : that, regarded purely psychologically, they
embrace the most various divergences from the norm in all
directions, — from the apathy of idiocy, which is only to be
moved by the most intensive sense-impressions, to the enormous
excitability of delirium, when the slightest external or internal
stimulation suffices to call up hallucinations and misleading
illusions ; or from the deep depression of melancholy, which
clouds the present and the past alike, to the bursts of maniacal
passion and the immovable cheerfulness of paralysis. The
deviations from the normal train of ideas will, of course, be
correspondingly different ; its course will be too quick or too
slow, too crowded or too sparse, as the case may be. And
these deviations stand in an intimate relation to emotional
changes ; they are not really disturbances of which these latter
are independent, but the two derangements are both implied in
any mental disturbance. In melancholy and paralysis alike,
the train of ideas moves haltingly, arrested by definite impres-
sions and memories, only that the affective colouring is wholly
different ; while in mental exaltation and mania it is accelerated,
springing from topic to topic without order or control.

All the more noteworthy is it, then, that, despite all these
differences, the departure from the norm is constant in one
particular respect, — in regard to the relation of associations to
the intellectual processes. If there is any single criterion of

318 Lectures on Human and Animal Psychology

.mental derangement, it is this, — that logical thought and the
voluntary activity of the constructive imagination give way to
.an incoherent play of multifarious associations. If the de-
rangement has not gone very far, — e.g., in the first period of a
slowly developing disease, — this change in conscious content
may be hardly noticeable, either because long intervals of
sanity interrupt the progress of the derangement, or because the
latter appears to confine itself to some particular ideational and
affective connection. But even in these cases, borderland-
cases, midway between the normal and the abnormal, where a
good natural constitution may more than hold in check the
encroachments of a disease, — even in such cases there can be no
doubt that from the moment at which consciousness is over-
come by the derangement the normal equilibrium of association
.and active apperception is once for all destroyed.

The most general way in which this disturbance of equilibrium
manifests itself is by a defective concentration of the attention.
It arises from the liability of the intellectual processes to be
continually interrupted by sudden associations. And the states
of mind in which the patient is always concerned about
particular impressions, or feelings are only an apparent ex-
ception to this rule. When the melancholiac broods incessantly
•over the crushing sorrow which he supposes himself to be ex-
periencing, it is not that he voluntarily directs his attention upon
it, and so controls the direction of his thoughts ; his mind is
dominated by an ever-present group of intensively toned ideas,
against which the will struggles often enough, but struggles in
vain. In the condition of mental exaltation we have an un-
naturally strong excitation of the sense-centres, giving to the
associational contents the character of external sense-impres-
sions ; so that these associations, which normally make against
the influence of the active attention, are rendered unusually
powerful. Ideational assimilation plays an especially large part
in this case. In normal mental life the assimilating elements
are just strong enough to render acts of cognition and recogni-
tion possible ; in hallucination they become so potent as to
throw the sense-impression into the position of a mere external
accident, which sets in motion ideational tendencies that have
not the remotest resemblance to itself.

Mental Derangement 319

Notice the way in which the insane express their thoughts.
Their language is abrupt ; it will vacillate in a purposeless way
between the most heterogeneous subjects, or it will come back
again and again to the same topic, for no assignable reason.
All this is not hard of explanation, if we suppose a lack of
voluntary control over the unruly crowd of associations. Of
•course, this lack of control may exist in very different degrees,
irom the eccentricity of thought which just oversteps the norm
to the wildest flights of fancy, in which thought follows thought
without the possibility of the mind's dwelling for even a short
time upon any. The last stage is a total incapacity to frame
any judgment that is at all complex. The patient begins to
utter some sentence. But his attention is taken captive by new
sense-perceptions, or by some extraneous circumstance, perhaps
by associations aroused by the sound of his own words. So
another and heterogeneous train of thought is set going, only
to be interrupted in its turn by still other associations. And
so the mad hurry goes on, until mental exhaustion puts a
temporary end to the tangled drift of ideas.

When we consider the vast importance of language for the
•development of thought, we can understand that associations of
words and sounds play the leading part among the thousand
forms of ideational involvement in the fancy-flights of the
insane. Words of like sound are heaped together in meaning-
less confusion in the middle of a sentence ; or a word will
suggest some totally heterogeneous thought, in which it also
happens to occur. So that the speech of the insane is our best
•opportunity to observe ' similarity '- and ' contiguity-associa-
tions ' in simultaneous and successive form, and with the utmost
variety of content. But it not seldom happens that when the
.flight of ideas is covering a large range of topics some particular
word will call up not another word, but perhaps simply a series
of articulate sounds, belonging, it may be, to like-sounding
words, or contained in others which have accidentally become
connected with the first. When this is the case, the language
of the insane becomes an unintelligible jargon, composed of
.articulate sounds that occur in real speech, but putting them
into quite new connections. There may then arise in the
patient's mind the delusion that he is speaking a previously

320 Lectures on Hitman and Animal Psychology

unfamiliar language, an idea which in its turn may give rise to
other delusions. But if we consider with some attention the
bewildering confusion of sound-conglomerations whose genesis
we have traced, we shall see that even here the influence of
practice, so important for association in general, is distinctly
traceable. The more frequently a particular sound- complex
has been repeated, the greater is the inclination to utter it
again. More especially does it tend to enter into fresh associa-
tions, whether with other sounds or with external objects ; and
so there may arise a dialect of insanity which in certain of its
constituents possesses all the characteristics of a new-formed
language : certain sounds or sound-complexes become de-
terminate symbols of definite concepts. At the same time we
can hardly say that this language is the invention of the insane.
It owes its origin to the blind chance of associational activity ;
and this continues to modify it in the most haphazard way.

There is scarcely anything more interesting to the psycholo-
gist than the observation of the gradual decay of the intellectual
functions as manifested in the language of the insane. Written
records are even better for this purpose than oral speech, for
the torrent of words, which must flow with incredible rapidity
to keep pace with the flights of fancy, cannot readily be
followed. There are printed works extant in all literatures
that declare themselves as products of a deranged mind. In
them we have most beautifully demonstrated the separate
trains of association, their intrusion upon the course of logical
thought, the gradual disintegration of this latter, and not
infrequently the influence of hallucinations and fantastic mis-
interpretations of sense-impressions. The final stages of this
mental decay are, of course, usually lacking ; but all the rest
are there. But I chanced once to pick up a book, — ' privately
printed for the author,' as you can imagine, — in which nearly
every stage of the process of disintegration, from one end to
the other, could be clearly traced. Its opening sentences are
correct in form and expression, although their content shows
from the first the beginnings of abnormal thought. Then
follow, with increasing frequency, descriptions of unmistakable
hallucinations and linguistic solecisms, while the intrusion of
disconnected associations makes itself more and more evident ;

Mental Derangement 321

till finally, on the last few pages, there is not a single sentence
that is brought to its correct grammatical conclusion.

When we subject these phenomena to a careful analysis,
especially as they are exhibited in such permanent form in
productions of the diseased mind which are more accessible
to investigation than the spoken word, we see at once how
inexact and superficial it is to speak of them as due to 'a lower-
ing of the mental functions.' As regards the flights of fancy
for instance, the mental functions are rather raised in a par-
ticular direction than lowered. The normal mind has not at
its disposal anything like such an abundant supply of associa-
tions as is not seldom met with in mental derangement. At
the same time, it is in this very mobility of association that
the germ of decay is to be looked for. It is the unfailing
symptom of the weakening of voluntary control over all those
connections of the ideational elements which the manifold
ramifications of the associational network render possible in
consciousness. We may safely say that no intellectual function
is possible until these relations and connections have been
collected from previous impressions. But, nevertheless, mental
activity only becomes intellectual when the total force resulting
from the whole sum of these previous experiences, the will,
controls and gives definite shape to the associative material
lying to its hand. In relation to these associations, the will
is at once an active and an inhibitory force, — it furthers the
connections concerned in the predominant interest of the
moment, while it inhibits all that might draw the attention
some other way. You see, then, that a sane man may volun-
tarily call up experimentally, as it were, a train of ideas which
very nearly corresponds to that of the insane. He has simply
to repress the regulative and inhibitory function of the will with
regard to the associations which crowd into consciousness. Put
yourselves in this condition, and write out the thoughts and
ideas which come to you ' of themselves ' ; you will have an
inextricable tangle of fragments of half-completed thoughts,
of chance impressions, with here and there a new-formed
association, — a picture that you might easily take to be that
of a deranged mind.

It is true that this luxuriant growth of associations, which

y

322 Lectures on Human and Animal Psychology

dwarfs the intellectual functions as creepers cramp and st ,nt
the trees that they entwine, is not a permanent condition. If
the process of derangement continues, the associations beco»ne
increasingly restricted to fewer and more stable ideas, which
repeat themselves over and over again. These ' fixed ' ideas,
called up in the first place by the particular tendency of the
diseased mind, become more and more insistent as the process
of associative practice keeps even pace with the general dis-
integration. When these fixed associations become exclusively
dominant in consciousness, the influence of the will is destroyed
once and for all. At the same time, the patient becomes less
responsive to external stimuli. The emotional depression con-
sequent on disquieting hallucinations, the affective disturbances
caused by painful impressions, disappear as the sensibility
becomes less, and the general mental dulness greater ; and give
way to a mood of uniform cheerfulness or indifference. And
with that is reached the final stage of mental derangement,
the saddest for the observer, the most happy for the patient
himself.

LECTURE XXII

§ I. DREAMS. § II. SLEEP-WALKING. § III. HYPNOTISM AND SUGGES-
TION. § IV. AUTOSUGGESTION AND POST-HYPNOTIC INFLUENCE.
§ V. ERRORS OF THE ' HYPNOTISM-PSYCHOLOGY.' § VI. THEORY
OF HYPNOTISM AND SUGGESTION.

§ I

WE have seen that a person of sound mind is able of his
own will to give himself up to the play of association,
and so induce a state of mind which more or less resembles
the ideational condition of the insane. That is not all, however.
We are all of us normally subject to experiences which bring
us still closer to a realisation of mental disturbance. One such
condition of what we may call normal temporary insanity is
that of dreaming.

In every relation of life we find the omne ignotum pro wag-
nifico borne witness to. Mankind tends always to regard the
unaccustomed as more wonderful than the usual and normal
The glamour of mystery surrounds the unfamiliar, just because
it is unfamiliar ; while the commonest phenomena, which so
often present the really most difficult problems, are looked
upon as matters of course. Former ages regarded the insane
as favoured of Heaven and illuminated above their fellows, or
as possessed of devils, — according as the pendulum of circum-
stance swung. And even to-day the subjective ideas of these
unfortunates are at times affected by such thoughts : thoughts
which arose in the first place from the contemplation of mental
derangement in its various forms. Even after this view had
died out as regards insanity, dreams were still invested with
something of the miraculous. The popular belief in premoni-
tion by dreams we need not notice. But there are still philo-
sophers who incline to think that when we dream the mind

323

324 Lectures on Human and Animal Psychology

has burst the fetters of the body ; and that dream-fancies
transcend the activity of the waking consciousness, with its
close confinement to the limits of space and time.

An unprejudiced observation of the phenomena of dreaming
must convince us that, beautiful as these theories are, they are
pretty nearly at the opposite pole from truth. When we are
awake, we are generally able by an effort of will to overcome
petty bodily distractions without much difficulty. The dreamer
is absolutely at their mercy ; the train of his ideas is diverted
by every chance impression that affects his senses, by every
accidental association. The commonest causes of the most
vivid dreams are indigestion, palpitation of the heart, difficulty
of breathing, and troubles of that sort. It is a matter of
dispute whether there is any such thing as dreamless sleep ;
and it will probably always remain so, seeing how easily we
forget what we have dreamed. But it is certain that if such
a state does occur, it will be most easily found in cases where
all bodily stimuli are wanting, or where they are at least
too weak to call up ideas.

The physiological nature of sleep we need not stop to discuss.
But little is known about it, if we except the general fact that
sleep is one of those periodic vital phenomena which originate
without exception in the central nervous system.* There is also
one fact that is psychologically important in a teleological
consideration of life : that during sleep there takes place a
reparation of the forces expended in the waking state by the
functioning of the various organs. Sleep is not seldom hin-
dered in the performance of this important duty by its attend-
ant, the dream. Vivid and unrestful dreams will detract
from the refreshing effect of sleep. The actual phenomena of
dreaming, however, make it probable that its greater or less
interference with sleep is due to a greater or less degree of
abnormal irritability in the sense-centres of the brain or in
particular parts of them ; this in its turn being caused, perhaps,
by a disturbance of the intracranial circulation. A confirma-
tion of this view is found in the fact that pathological altera-
tions in blood and blood-supply (such as occur, e.g., in fever)
may considerably intensify dream-phenomena, and even occa-
sion similar mental conditions, those of febrile delirium, in the
waking state.

Dreams 325

We have already, then, in outline the essential characters
of the dream-idea. It is a hallucination ; its intensity is as
great as that of a sensation given in direct perception, and it
is as such that it is regarded by the dreamer. The principal
dream-constituents are memorial images, but memories which
are interwoven altogether at random, — whether they refer to the
immediate past or to some more remote experience, whether
they belong together or are wholly unrelated, — by the unregu-
lated play of association. Dreaming has, therefore, at first
sight, some resemblance to the normal activity of imagination ;
it tends to combine memory-ideas in new and unaccustomed
ways. But it entirely lacks that purposive arrangement and
grouping of ideas which is the one criterion for the discrimina-
tion of imagination from the activity of memory.

The world of memory and the world of dreams are alike
dominated by ideas of sight. Auditory ideas are also found
to occur. No other sense appears to furnish dream-material
to any considerable extent except when directly stimulated
from without. Of course, there may be direct external excita-
tion in the cases of sight and hearing also ; and indeed it is
probable that dream-ideas are aroused in this way far oftener
than is generally assumed. It may even be that the predomi-
nance of the visual idea in the world of dreams is to be
accounted for not solely by the very great importance of sight
for memory, but also by the peculiar nature of the eye, which
is more exposed than any other sense-organ to the continual
operation of weak external stimuli. If we look attentively
at the darkened field of vision of the closed eye, we notice
an unceasing appearance and disappearance of light-pheno-
mena : now single points of light will shoot like meteors from
side to side ; now a veil of twilight is drawn across the blacker
background ; now again parts of this appear in the most
brilliant colours, There can be no doubt that these pheno-
mena persist during sleep to call up the memory-images that
resemble them, and of which consciousness possesses so large
a store.

Dreaming, then, is related to the train of ideas in the waking
consciousness in that its proximate cause is usually some
external sensory excitation, to which memorial images readily

326 Lectures on H^l'^nan and Animal Psychology

attach themselves. But in two respects the processes are very
different. The ideas called up by the sense-impressions are
more or less fantastic illusions ; and the consequent successive
associations do not possess the character of ordinary memory-
images, but of hallucinations: and, like these, they are taken for
actual experiences. It is, therefore, very seldom, — if at all.
only at the moment when sleep is passing over into waking, —
that we dream of remembering anything. Dreaming is as
immediate as any experience can be. It shows no trace of
the usual discriminatory marks of imagination and reality.

If dreaming reminds us, from this point of view, of mental
disturbance, it has one characteristic which does not appear
in the same degree in any of the manifold forms of insanity, —
its complete restriction to the ideas of the immediate present.
The illusions or hypostatised memorial images of the deranged
mind can never do more than partially prejudice the normal
apprehension of an object ; while there is a clear distinction
drawn between them and the customary activity of imagination
and memory. And dreaming occupies a peculiar position in
yet another respect. If we look at the part played in it by
hallucination, we shall be inclined to parallel it with the initial
stages of certain mental disturbances, which bring with them
an abnormal excitability. But in the incoherence of dream-
ideas, in the clouding of judgment and the lapse of self-
consciousness, we have a series of phenomena which only find
a parallel in the most extreme forms of mental disorder.
Probably the greater number of dreams come and go without
involving any really intellectual process at all. The dreamer
acts, or looks on at action, without ever making his experience
the subject of reflection. It is generally when dreaming is, as
it were, dovetailed in with waking, — just before we fall asleep
or shortly before waking, — that a real activity of intelligence
is noticeable : we make dream-speeches, or carry on dream-
conversations. But the language used is of a curiously mixed
kind. Sometimes there is an almost normal capacity of con-
nected expression, though when we analyse we find that the
dream-speech consisted entirely of familiar phrases and current
turns of language. Sometimes there is no normal connection
in the thoughts uttered ; the whole is a strange medley, the

Sleep-walking 327

judgments meaningless, the conclusions wrong. It may be that
the confusion of thought extends even to the sound of the
words employed ; so that we have new formations of articulate
syllables, like those which occur in the talk of the insane. And
these are connected, by the way, with the same set of subjective
ideas ; the dreamer, like the maniac, thinks that he is speak-
ing fluently a new and unknown language, or perhaps some
real language, which he has actually studied, but only very
imperfectly mastered.

All these phenomena tend to show that the relation of the
intellectual functions to associations in dreaming is altered very
much as it is in the more advanced stages of mental derange-
ment. The control of the will over the mob of ideas and
feelings has been abrogated. The dreamer is completely at
the mercy of associations instituted by accidental external
impressions. And, in addition to that, the hallucinatory
character of dream-ideas gives them their peculiar ability to
pass for real experiential events.

A special kind of dreaming, which is generally a symptom
of an abnormal excitability of the nervous system, is sleep-
walking. It is a dream carried one step beyond the halluci-
natory conversations mentioned above. For sleep-walking con-
sists simply in this : that the connections between conscious
states and external voluntary acts which hold in our waking
life are realised to the same extent during sleep. And since,
of all these connections, that of idea with the muscles sub-
serving language has become the most customary and auto-
matic, we can understand that these will be most often and
most readily exercised. Sleep-walking, then, like dreaming,
has nothing mysterious about it ; it is simply an event of
infrequent occurrence, which for that very reason has sometimes
been looked upon as inexplicable. Indeed, when we consider
the character of the connections obtaining between sensations
and the movements which they stimulate, it becomes rather
a matter for surprise that dream-walking is not a far commoner
phenomenon than it is. We may explain the facts in one of

328 Lectures on Human and Animal Psychology

two ways. We can assume either that the sensory centres an,
more exposed during sleep to the operation of the various
causes of excitation than the motor centres are, or that the
latter are in general subject to certain inhibitory influences.
However this may be, there can be no doubt of the very great
utility of this separation of the world of dream-ideas from the
sphere of external action. Think what would happen if we
actually did everything that in our dreams we imagine we
are doing !

But sleep-walking presents other differences from ordinary
sleep. Especially worthy of note is an increased excitability of
the sense-organs in presence of external stimuli. The sleep-
walker sees and cognises external objects up to a certain
point. But his dream-perceptions are of an illusory character,
and so he misinterprets them: he may take the window for
the door, or the ridge of the roof for a boulevard. While,
therefore, he can perform simple acts, and especially such as
have become more or less automatic by practice, he will hardly
go beyond these. The tales that are told of wonderful dream-
performances, — the sleep-walking mathematician who solves a
difficult problem or the schoolboy who regularly does his
work in this very convenient way, — we may consign without
more ado to the limbo of the fabulous. No reliable observer
has ever confirmed reports like these ; and they conflict with
all that we know of the nature of dream-ideas in general.

§ HI

It is but a short step from sleep-walking to phenomena
which have lately formed the topic of much discussion, — the
phenomena of hypnotism. The principal condition for the
induction of the hypnotic state is a vivid idea of a passive
surrender of the will to that of some other person, who is
able to influence his subject by words, acts, or gestures. An
abnormal excitability of the nervous system favours this influ-
ence. But the experiment will, as a rule, succeed in the long
run even with persons who at the outset were proof against
it ; or, in other words, the frequent repetition of the state
facilitates its induction, and furthers the passage of the initial

Hypnotism and Suggestion 329

stages into the higher. Other conditions which have often
been regarded as auxiliary or as the sole causes of hypnosis, —
especially weak and uniform stimulation : the steady gazing
at an object, the ' magnetic ' stroking of the skin, and so
on, — are, obviously, only secondary and indirect means to the
end. They serve in part to weaken the active attention, in
part to arouse the idea of an influence militating against the
independence of the subject's volition. It was proved by the
cures worked by Mesmer and his successors in terms of ' animal
magnetism ' (which is in essentials just the same thing as
hypnotism) that it was necessary for the success of the experi-
ment that the patient should believe in the efficacy of the
strokings and other manipulations, but that this belief was
sufficient ; so that the passes and all the rest of it might be
left out, if only the subject thought that they were there.

The symptoms of hypnosis vary according to the stage which
the condition has reached, and the susceptibility of the subject.
We can distinguish three degrees of it, which, from their resem-
blance to the corresponding stages of normal sleep, have been
termed drowsiness, light sleep, and deep sleep. The similarity is,
however, confined to merely external characteristics, and in
particular obtains only for the appearance and behaviour of
the subject before definite influences are allowed to play upon
him and assume control of his perception and volition. It is
this possession, as we may term it, which really differentiates
the two states. Even in the light hypnotic sleep 'suggestion,'
— the influencing of ideation and volition from without, — begins
to play a part. The hypnotised subject cannot open his eyes
of his own accord, cannot perform any voluntary movement
whatever, though he recovers this power the instant that an
action is suggested to him by a word of command from the
hypnotiser. The skin is anaesthetic, which is never the case
in sleep ; so that needle-pricks are often not sensed at all, or,
if they are, only as pressures from blunt points. Conjoined
with anaesthesia we find all the various phenomena of 'auto-
matic reaction to command.' The subject executes movements
that are suggested to him, puts his limbs in the most uncom-
fortable positions, and keeps them there until another command
suggests relaxation. In many persons a rigid or tetanic state

33O Lectures on Human and Animal Psychology

of muscles appears even in the absence of suggestion. On
waking, — the hypnosis can be dispelled instantaneously by a
word from the operator, — the subject generally retains some
sort of cloudy recollection of what occurred to him during his
s'eep.

This power of recollection serves to distinguish the lighter
from the deeper hypnotic sleep, — somnambulism, as it is also
called, — after which the memory is a simple blank. All the
other symptoms are also much exaggerated. The automatic
reaction in particular extends beyond movement to sense-per-
ception. The somnambulist will objectify any ideas that are
suggested to him. There are two proofs of the intensification
of ordinary fancy-images, arbitrarily aroused by the suggestion
of the hypnotiser, to hallucinations : first, this confusion be-
tween imagination and reality, and secondly, the production of
complementary after-images of the suggested perceptions. Here
is a particular observation to illustrate the second fact. The
operator calls out to the subject, ' Look at that red cross on
the wall ! ' When the latter has found it, he is told to look
on the ground, and asked, ' What do you see there ? ' The
answer is, 'A green cross.' That is, the after-effect of the
hallucination is just what that of the actual impression of a red
cross would have been (cf. p. 109). Illusions of taste are also
very easily induced. The subject will take a glass of water for
champagne, and drink it with every sign of satisfaction ; while,
if he is told a moment after that he has been drinking ink, he
will spit it out with equally evident marks of disgust. At the
same time I am not sure that all these are cases of real hallu-
cination. When we consider how very rarely hallucinations of
smell and taste occur in dreaming, we shall be inclined to think
that in these instances of suggestion too the sensations com-
posing the ideas may be confined to those of mimetic movement.

§ IV

There are many other phenomena, manifested especially in
the somnambulistic stage, which have often been employed to
shroud the hypnotic sleep in the veil of mystery and wonder.
Thus a suggestion may very readily lead to the formation of the
idea that the subject is to obey the suggestions and commands
of one person only, generally of the operator, while remaining

Autosuggestion and Post-hypnotic Influence 331

indifferent to any attempt at influence on the part of others.
There then arises what the animal-magnetism school term the
rapport of the medium with the magnetiser. This is really, as
we have indicated above, only the result of a secondary sug-
gestion, which is favoured by the special circumstances of the
induction. The exclusive direction of the attention of the sub-
ject upon the operator is itself at times sufficient to produce
this rapport, even without any express command, especially if
he is always put to sleep by the same person, as is of course
the case in the instances of ' magnetic ' cure. There is no
intrinsic reason, that is, why the hypnotic subject should not be
accessible to other influences. Without them we should be unable
to explain the fact of autosuggestion. Autosuggestion implies-
an abnormally strong tendency towards hypnosis. Frequent
hypnotising may lead in the long run to an irresistible passion,
for the hypnotic sleep, in which case the impulse to obtain it
acts like the morphine-habit or habituation to any particular
stimulant or sedative. The confirmed hypnotic will try in every
possible way to procure the enjoyment which he craves. And
he has in autosuggestion, when he has once discovered how to
use it, a means lying always ready to his hand. By voluntarily
arousing and fixing the idea that he will fall into the hypnotic
sleep, he can induce all the phenomena that ordinarily accom-
pany it. It appears, moreover, that in the condition as brought
on both by autosuggestion and by suggestion from without
there may be a continuous memory from sleep to sleep, such
as is sometimes observed in dreaming and in certain forms of
periodical mental derangement. The psychology of the act
of recollection gives us the key to the explanation of this pheno-
menon. It is wholly unnecessary to assume the existence of a
mysterious mental double, the 'other self or second personality,
or to set up any other of the fanciful hypotheses so plentiful in
this field. There is, as you know, one invariable condition of
the occurrence of an act of recollection : — if we wish to bring
about a complete renewal of a past experience, we must repro-
duce the whole of the ideational and affective content of con-
sciousness which characterised that experience. Now, since there
is a great difference between the waking consciousness and that
of the hypnotic sleep and since the difference increases with

33 2 Lectures on Human and Animal Psychology

the progress of that sleep, we can readily understand that its
suggestions will be forgotten on waking ; while we also see how
the recollection of those suggestions will be possible when the
hypnotic state is renewed.

Many cases of the post-hypnotic effects of suggestion appear
explicable on these two principles of the conditions of memorial
functioning and of autosuggestion. When, e.g., it is suggested
to a somnambulist that he will perform a definite action at
some particular time of another day, — take a certain walk, exe-
cute a given order, mix a special draught and offer it to some
third person who is described in detail, — the idea recedes into the
background of consciousness at the moment of waking ; but,
as the appointed time draws near, comes up again in obscure
form, as the 'feeling' that something particular is going to
happen. This idea of the time of the performance of the action,
usually furthered by special insistence upon it in the primary
suggestion, is still more intensified, in accordance with the
general laws of association, when the time actually arrives ; and
from this moment the indefinite idea of a commission under-
taken,-— what commission is still wholly unknown, — exerts an
autohypnotic effect, There follows a partial revival of the
somnambulistic state, sufficient to re-excite the memory of the
suggested ideas, and at the same time to exclude any considera-
tion of the motive or purpose of the action. This is then
performed in an automatic, lethargic condition, which, however,
as an imperfect repetition of the previous complete somnam-
bulism, does not preclude the memory of it in the normal
waking state. Asked why he did so-and-so, the awakened
subject is unable to give any explanation ; or simply says that
he could not help it, or that it was suggested to him in sleep,
the latter answer giving clear evidence of a persistence of the
suggested ideas in an obscure form into the waking state.
Where the post-hypnotic effect takes place immediately after the
awaking from somnambulism, it is probably the direct result of
this persistent operation on the part of the suggested ideas. It
looks sometimes, under these circumstances, as though the sub-
ject were not really fully awake ; his behaviour is more like that
of a person just aroused from ordinary sleep. Indeed, those of
you who are subject to very vivid dreams may now and again

Autosuggestion and Post- hypnotic Influence 333

observe quite analogous phenomena when you are suddenly
awaked from one. You think and act for a short while in terms
of the preceding dream-ideas ; but waking impressions keep
continually mixing with them, until at last they gain the upper
<iand, and you are fully awake.

But it is plain enough that autosuggestion cannot be the
exclusive cause of post-hypnotic effects. When it is a question
of executing some simple order directly after waking, or after
che lapse of a definite time, the actions very frequently follow
without any symptom of a partial relapse into hypnosis. We
must therefore suppose that the suggested idea, with its corre-
sponding motor impulse, may be latently operative in conscious-
ness ; so that it will come to the conscious fixation-point either
immediately after waking or at the time suggested. It will
then, like every other impulse, continue to exert its influence
until the action results, or it is inhibited by opposing forces of
the waking consciousness, themselves impulses, sensory or in-
tellectual. This view is confirmed by the frequent occurrence
of phenomena of resistance, often successful, to the performance
of the suggested action. At the same time, there is positive
proof that even here consciousness does not at once return to
its normal condition, — proof furnished by post-hypnotic hallu-
cination. The awakened somnambulist, in obedience to sug-
gestion, may see the operator in fanciful costume, perhaps
with a red cloak over his shoulders and horns upon his head ;
he will find a flower in his buttonhole which is not there ; or he
will overlook a doorway, and declare that the room has no
outlet. It is obvious that such hallucinations and illusions
require us to assume an extreme excitability of the sensory
centres, such as certainly does not exist after waking from
normal sleep.

You are familiar with the very astonishing cures now and
again worked by physicians who employ hypnotism therapeu-
tically. These must be referred to the post-hypnotic effects of
suggestion. It cannot be disputed that a cautious and intel-
ligent use of suggestion may be of avail for the temporary,
perhaps even for the permanent, removal of diseases due to
functional derangement of the nervous system, or to harmful
practices, like alcoholism or the morphine-habit. But it is an

334 Lectures on Human and Animal Psychology

equally undeniable fact that suggestion is in the long run just
as ineffective for the cure of diseases arising from some palpable
pathological cause as would be any other form of command to
the patient to grow well again.

There is, indeed, one exception to this rule, — an exception
which is explicable from well-known physiological facts. Mental
influences may, of course, affect the functioning of the bodily
organs, and especially the excitations of the vasomotor and
secretory nerves. And suggestion takes rank with other mental
influences in this regard, becoming increasingly efficacious as
the subject surrenders himself more and more permanently to
the power of the suggested ideas. Thus an arrest of any par-
ticular secretion, — provided always, again, that the derangement
is not due to pathological conditions seated in the organ itself,
— may be overcome under the influence of suggestion. Dilata-
tion of the blood-vessels, with all its consequences, may be
suggestively induced, particularly if actual external stimuli are
present to help produce the effect. An innocent scrap of
postage-stamp paper, stuck upon the skin, has been known to
answer all the purposes of a blister, if the idea were suggested
that it was really a blister which was being applied. It is true
that these phenomena cannot be obtained in the case of every
hypnotised subject, or even of every somnambulist: the right
disposition is requisite for the manifestation of such intensive
organic effects. As for the physiological results of suggestion in
themselves, they are simply more intensive and permanent forms
of familiar and universal relations existing between mental states
and bodily processes. If the transient emotion of shame can
normally bring about a temporary distension of the blood-vessels
of the face, it is alter all not surprising that an abnormal excita-
bility of the vasomotor and secretory nerve-system, combined
with a domination of consciousness by ideas and feelings tending
definitely to oppose the accompanying mental disturbance,
should condition a more intensive and permanent physiological
reaction to mental stimulus. And in saying this we are stating
that hypnotism as a therapeutic agency is a two-edged instru-
ment. If its effects are strongest when the patient is predisposed
to it in body and mind, or when suggestion has become a settled
mode of treatment, it may obviously be employed to intensify

Errors of the 'Hypnotism-psychology ' 335

or actually induce a pathological disposition. It must be looked
upon, not as a remedy of universal serviceability, but as a poison
whose effect may be beneficial under certain circumstances. We
find, of course, not only the dabbler in hypnotism, — who has no
claim to a judgment on the question, and in whose hands the
practice of suggestion becomes a public nuisance, — but also the
physician, — to whom thinking men will no more deny the right
to employ this dangerous remedy in certain circumstances than
that of using any other, — asserting that the hypnotic sleep is not
injurious, because it is not in itself a pathological condition. But
surely the facts of post-hypnotic hallucination and the diminu-
tion of the power of resistance to suggestive influences furnish
a refutation of this statement which no counter-arguments can
shake. It is a phenomenon of common observation that fre-
quently hypnotised individuals can when fully awake be per-
suaded of the wildest fables, and thenceforth regard them as

o

passages from their own experience.

§ V

But we are not concerned in this place with the physiological
effects of suggestion, and its consequent significance for thera-
peutics. For psychology the questions of special interest are
that of the alterations of consciousness occurring during the
hypnotic sleep, and, connected directly with this, that of the
nature of suggestion. The difficulty of the former lies in the
impossibility of actual introspection on the part of the hypnotic
subject. When aroused from the lighter form of hypnotic sleep,
he has no clear recollection of what has taken place ; while after
the somnambulistic state the memorial activity is in complete
abeyance. Observation is therefore more difficult here, if that
be possible, than it is in the case of dreaming. So there is all
the more opportunity for fanciful hypotheses, to which the lay
mind is tempted by the unusual and apparently mysterious
character of the phenomena. And the lay mind is unfortunately
an all too frequent possession of those who have desired to
make hypnosis the object of psychological observation. Most
hypnotic investigators are either physicians, who employ sug-
gestion for therapeutic purposes, or philosophers, who think that

336 Lectiires on H^lman and Animal Psychology

they have discovered in hypnotism a basis for new metaphysical
systems, and who, instead of examining the phenomena in the
light of well-established psychological laws, reverse the matter
and erect their psychological superstructure upon hypnotic
foundations. So that it is hardly to be wondered at that the
modern hypnotism-psychology has time and again manifested
its descent from spiritism. Clairvoyance and the magic of tele-
pathy play a suspiciously important part in it ; and though
there are found observers who have remained sane enough to
hold aloof from all these absurdities, many even of them evince
the fatal effect of the influence under which they have fallen
by declaring all these superstitions to be after all ' open ques-
tions,' which deserve, if they do not demand, a closer examination.
Like the scientific superstition of all times, this modern one
arrays itself in garments borrowed from real science. It deter-
mines the credibility of clairvoyant somnambulists, or the
occurrence of a telepathic miracle, by the rules of mathematical
probability. It terms this whole field of hypnotic mysticism, —
and here again it follows in the footsteps of the spiritism that
preceded it, — ' experimental psychology.' It organises ' societies
for psychical research,' which are devoted to the cult of hypnotic
experimentation. The chief danger of all this, it seems to me,
does not lie in the abuse of post-hypnotic suggestion for criminal
purposes which may happen once in a while. Crimes have
hardly as yet been committed by ' mediums ' as a result of
suggestion. No ! the great danger is, that persons of insufficient
medical training, working not for therapeutic ends, but ' in the
interests of science,' — though there is absolutely no guarantee
of the real existence of their scientific devotion, — may exert an
influence upon the mental and bodily life of their fellow-men
such as, if continued for any length of time together, cannot
fail to be injurious.

It must, moreover, be plain to you all that there can be no
question of an experimental psychological method, in the exact
sense of those words, in this matter of hypnotising. The con-
dition of hypnosis is such as absolutely to preclude the possi-
bility of a psychological experiment in the real sense. The
psychological experiment demands from its subject concentra-
tion of the attention, practice, skilled introspection, in short,

Theory of Hypnotism and Suggestion 3?^

the fulfilment of all manner of conditions, which, if not alto-
gether and normally out of the reach of the hypnotic subject,
is at least wholly impossible during the course of the induced
sleep. If we compose ourselves to sleep, with the intention of
observing our dreams so far as that is possible, or even if we
take morphine for the same purpose, we are not making an
experiment, not doing anything that in execution or result is
essentially different from simple observation. The conditions
of dream-observation are not altered in the slightest degree by
the fact that we have brought on sleep intentionally The cha-
racteristics of the experimental method are variation and grada-
tion of the phenomena, and elimination of certain conditions.
Such a mode of procedure can be followed out in artificially
induced sleep as little — or, let us say, as imperfectly — as in
natural sleep : we shall gain no more by investigating the former
than by collecting casual observations of normal dreams. And
all this holds in still greater measure of hypnotism, since just
in the cases which present the most interesting phenomena
there is a total absence of any subsequent recollection. We
can only infer what goes on in the mind of the somnambulist
from his words and actions ; if we wish to subject him to special
influences, we are hampered by the same conditions as hinder
the investigation of sleep and dreams.

§ VI

Any explanation of the phenomena of hypnosis must, ob-
viously, begin with the cognate facts of our normal mental life,
We have not to explain the usual functions of consciousness in
terms of hypnotism, but conversely. The established facts of
normal life, and especially those which best admit of introspective
control, must be employed to throw light on these phenomena,
which, if not pathological, are at least due to unusual conditions.
Now there is one state which you will see at once evinces a very
great similarity to the hypnotic sleep, — heaviness after waking.
In this condition we may perform actions, obey orders, answer
questions ; but when we have fully awakened we realise that
all this was done half automatically, without any assistance from
the will. »In other words, there may be developed an ' automatic

338 Lectures on Human and Animal Psychology

reaction to command,' very like that of the hypnotic subject.
The sleepy soldier acts automatically at the word of command ;
the half-roused servant executes a commission ; but it is only
when fully awake that either remarks what he has done: indeed,
if the sleepiness continues, he may entirely forget it. Years
ago, when I myself went through several such experiences, I
noticed particularly that I felt myself entirely at the mercy of
external impressions, and acted, under their influence and that
of the first dreamlike associations that they aroused, without
any consideration, and so without any consciousness of the
occasional wrongness of what I was doing. This self-surrender
to external impressions approximates the dream-state ; while
the capacity of action and the general absence of hallucinations
and illusions suggest, on the contrary, the waking condition of
consciousness. But this exemption is not altogether constant.
Illusions in particular frequently occur in the state of drowsiness.

Suppose now that the condition just described is brought
one stage nearer that of sleep, — suppose that the self-surrender
to external impressions results in exclusive conscious control by
definite ideas and feelings suggested by the operator, — and you
have the hypnotic sleep. One of the chief effects of suggestion
is to increase the duration of this state. The subject, who fell
asleep at the word of command or under the influence of ideas
equivalent to it, remains dominated by the idea that he cannot
wake except by a new command. So that the most marked
characteristics of hypnosis are loss of volitional initiative, re-
striction of the receptivity of consciousness to external impressions
and the first associations that they call up, and usually a deter-
minate direction of the attention induced by the influence of
the operator's suggestion. Its effects are intensified by the
tendency to hallucination, which, combined with the absolute
surrender to external impressions, results in a transformation of
the suggestions of the hypnotic consciousness into real objects.

You see, then, that the hypnotic sleep is akin to normal sleep
and dreaming, occupying an intermediate position between these
and drowsiness, but characterised by the surrender of our will
to that of another person, and by the consequent efficacy of
suggestion. Especially to be noticed is the inhibition of volun-
tary activity. This is not only one of the chief dtagnostic

Theory of Hypnotism and Suggestion 339

symptoms, but an important condition of the origin of the other
phenomena. You must not, however, imagine that will-power
is altogether in abeyance. Hypnotic actions are always volun-
tary actions in the wider sense of the word. But they are not
self-initiated, resulting from a consideration of motives and a
decision of the agent's own mind ; they are impulsive, univocally
determined by a suggested idea and by the associations which
it directly excites.

Regarded from the point of view of will and voluntary action,
then, the hypnotic sleep is an abnormal condition. But it is a
condition which follows all the psychological laws of our waking
life. And the same is true of suggestion, that other so significant
factor in the origin and progress of hypnosis. Ideas are con-
tinually aroused in our minds by the words which we hear and
the actions which we see. Word and act are intimately associ-
ated with ideas, and affect our mind and will with all the greater
force the smaller the number of conflicting associations or
inhibitory intellectual motives that opposes them. Looked at in
this way, suggestion reduces itself simply to an external impres-
sion, followed by associations characterised less by definite and
positive attributes than by the negative quality of the absence
of inhibitory influences. This impression and the consequent
ideas will, therefore, continue to be the exclusive determinants
of volition until other suggestions (i.e., other similarly excited
associations) give a contrary direction to the hypnotic conscious-
ness. How these facts enable us to explain certain special
forms of suggestion, — autosuggestion, post-hypnotic suggestive
influences, etc.,— I attempted to show in describing those phe-
nomena themselves.1

1 For the physiological substrate of the hypnotic condition, and for the
discussion of many other points which can only be briefly touched on here,
cf. my detailed account of hypnotism in the Philosophische Studien, vol.
viii., pp. I ff.

LECTURE XXIII

§ I. PROBLEMS OF ANIMAL PSYCHOLOGY ; DEFICIENCIES OF THE,
SCIENCE. § II. METHODOLOGICAL RULES. § III. ACTS OF COGNI-
TION AND RECOGNITION AMONG ANIMALS. § IV. ASSOCIATION

AMONG THE LOWER ANIMALS.

§1

IN the preceding lectures we have considered the associative and
intellectual processes of consciousness, first in their general
and normal features and then under the various aspects which
they present in mental disturbance, dreaming, and certain con-
ditions related to that of sleep and dreaming. There now
remains one last question, the answer to which is important if
we are to understand the nature of these processes and their
relation to the other functions of the mind, the question of
animal intelligence, or, to express it more exactly, of the nature
and significance of those animal actions the conditions of whose
origin lead us to refer them to mental processes similar to our
own associations, and possibly even to our own processes of
judgment and inference.

The study of animal psychology may be approached from
two different points of view. We may set out from the notion
of a kind of comparative jfhysiology of mind, a universal^

history of_the development ofwmental life in the organic world. [

Then the^observation of animalsjs the more important matter;
man is onlyconsMered as one, though, of course, the highest, of
the developmental stages to be examined. Or we may make
human psychology the principal object of investigation! Then
the expressions of mental life in animals will be taken into
account only so far as .they throw light upon the evolution
of consciousness in man. I You will remember that we decided
at the outset of these lectures to deal with animal psychology in
this second sense, ana for the more limited purpose.

Problems of Animal Psychology 341

If we compare these two ways of treating psychology with
comparative and human physiology, we cannot fail to see that
the two spheres of investigation are very different as regards
methods and appliances. The bodily organs and functions of
animals are just as accessible to objective examination as are
those of man . indeed, in the living condition for obvious reasons
far more completely so. So that there is no need to remind
human physiology that it must never omit the comparative
reference to animals. It follows this rule of its own accord,
oftentimes more than it cares to, or than might be wished in the
interests of physiological theory, because it must necessarily
have recourse to animals where observation on man is impos-
sible. Human psychology, on the contrary, may confine itself
altogether to man, and generally has done so to far too great an
extent. There are plenty of psychological text-books from
which you would hardly gather that there was any other con-
scious life than the human. , It is entirely different with com-
parative physiology and comparative psychology. It would" be
possible, if needs were, to write a monograph upon the physiology
of an order or a species, say the infusoria or the frog, without
paying any regard to the analogous functions in man. But not
the least advance can be made, either in the psychology of a
particular animal or in that of the animal kingdom, without
starting out from the facts of the human consciousness. And
here again it is psychology that has been at fault. Following
the analogy of comparative anatomy or physiology, psychologists
have attempted without more ado to schematise the evolution
ot mental life in animals, and then to apply their results directly
to that of man. The outcome could be nothing else than that
which always follows from the premature use in one connection
of concepts found in another. So that Bacon's comparison of the
insufficient observation of nature by the Aristotelians of his day
to the report of an ambassador who based his knowledge of the
measures of a Government upon town gossip, and not upon
accurate examination, applies fairly enough to the animal
psychology of our own time. It is permeated through and
through by the concepts of the every-day psychology, which is
thought to suffice for the requirements of ordinary life, and too
often also for the sciences which cannot do without psychological

34 2 Lectiires on Human and Amnial Psychology

reference. The one great defect of this popular psychology is,
that it does not take mental processes for what they show them-
selves to be to a direct and unprejudiced view, but imports into
them the reflections of the observer about them. The necessary
consequence for animal psychology is, that the mental actions of
animals, from the lowest to the highest, are interpreted as acts
of the understanding. If any vital manifestation of the organism
is capable of possible derivation from a series of reflections and
inferences, that is taken as sufficient proof that these reflections
and inferences actually led up to it. And, indeed, in the
absence of a careful analysis of our subjective perceptions, we
can hardly avoid this conclusion. Logical reflection is the
mental process most familiar to us, because we discover its
presence whenever we think about any object whatsoever. So that
for popular psychology mental life in general is dissolved in the
medium of logical reflection. The question whether there are
not perhaps other mental processes of a simpler nature is not
asked at all, for the one reason that, whenever self-observation is
required, it discovers this reflective process in the human con-
sciousness. The same idea is applied to feelings, impulses, and
voluntary actions, which are regarded, if not as acts of intelli-
gence, still as affective states which belong to the intellectual
sphere.

This mistake, then, springs from ignorance of exact psycho-
logical methods. It is, unfortunately, often rendered worse by!
the inclination of animal psychologists to see the intellectual
achievements of animals in the most brilliant light. This, of
course, is due to the natural pleasure which the objects of our
observation always give us, and which is the most effective spur
to continuous devotion to a particular subject. In the present
case it is transformed into the unintentional endeavour to
observe things which shall be as interesting as possible. Un-
bridled by scientific criticism, the imagination of the observer
ascribes the phenomena in perfectly good faith to motives which
are entirely of its own invention. The facts reported may be
wholly true ; the interpretation of the psychologist, innocently
woven in with his account of them, puts them from first to last
in a totally wrong light. You will find a proof of this on nearly
every page of the works on animal psychology. Take a few

Problems of Animal Psychology 343

instances, chosen at random, from Romanes' industriously com-
piled volume on Animal Intelligence. x While we admire the
diligence with which the author has observed and collected the
observations of others, we cannot but notice the unfortunate
absence of the critical attitude in a field where it is especially
desirable. Turn to the chapter on ants. An English clergy-
man writes apropos of the ' funereal habits ' of these animals :
' I have noticed in one of my formicaria a subterranean
cemetery, where I have seen some ants burying their dead by
placing earth above them. One ant was evidently much
affected, and tried to exhume the bodies ; but the united exer-
tions of the yellow sextons were more than sufficient to
neutralise the effort of the disconsolate mourner ' (p. 92). How
much is fact, and how much imagination ? It is a fact that the
ants carry out of the nest, deposit near by, and cover up dead
bodies, just as they do anything else that is in their way. They
can then pass to and fro over them without hindrance. In the
observed case they were evidently interrupted in this occupation
by another ant, and resisted its interference. The cemetery, the
sextons, the feelings of the disconsolate mourner, which impelled
her to exhume the body of the departed, — all this is a fiction of
the sympathetic imagination of the observer. Another friend
of the ants gives this account : ' At one formicary half a dozen
or more young queens were out at the same time. They would
climb up a large pebble near the gate, face the wind, and assume
a rampant posture. Several having ascended the stone at one
time, there ensued a little playful passage-at-arms as to position.
They nipped each other gently with the mandibles, and chased
one another from favourite spots. They, however, never nipped
the workers. These latter evidently kept a watch upon the
sportive princesses, occasionally saluted them with their antennae
in the usual way, or touched them at the abdomen, but
apparently allowed them full liberty of action ' (p. 88). The
correctness of this observation need not be questioned. Why
should not a number of young queens have been crowded
together upon a pebble, and some workers have been with them,

1 Animal Intelligence, by G. J. Romanes, Int. Sci. Series, vol. xli., 4th ed.
(1886). Cf. the same authors Mental Evolution in Animals (i88;\

344 Lectures on Hitman and Animal Psychology

and occasionally touched them with their antennae, as ants do
everywhere ? But that they ' sported ' and played, that the
others ' kept a watch upon them ' like chaperones, and now and
again did homage to them by ' saluting,' — that, again, is all due
to the imagination of the observer. He would hardly have told
the story as it stands had not zoology introduced the mislead-
ingly suggestive term ' queens ' for the mature female insects.
If the adults are ' queens,' the young females must, of course, be
' princesses.' And since no princess ever went but without an
attendant or a chaperone, the rest of the narrative follows as a
matter of course. Written in jusi the same style is the follow-
ing account of the education of ants, taken from the same work.
It may serve at the same time as an instance of the more
general remarks current in the literature of animal psychology.
' The young ant/ the author tells us, ' does not appear to come
into the world with a full instinctive knowledge of all its duties
as a member of a social community. It is led about the nest,
and " trained to a knowledge of domestic duties, especially in
the case of the larvae." Later on the young ants are taught to
distinguish between friends and foes ' (p. 59). These illustra-
tions will enable you to judge how much of similar descriptions
is actual fact, and how much is due to the imagination of the
observer.

How easy it is to misinterpret an observation if the very
greatest care is not taken in recording it, and if it is impossible
to vary the circumstances by experiment, and so obtain accurate
knowledge of its conditions, is well shown by the following facts.
Pierre Huber, one of the most reliable students ol the habits of
ants, stated that he had assured himself that an ant, if taken
from the nest and returned after an interval of four months, was
recognised by its former companions ; for they received it
friendlily, while members of a different nest, even though they
belonged to the same species, were driven away. Huber regards
this as evidence of the extraordinary accuracy of memory in these
insects. Now the correctness of his observation cannot be
doubted ; and, besides, it has been confirmed by another
experienced investigator, — Sir John Lubbock At first sight,
therefore, the conclusion seems perfectly justifiable. But if a
single individual were really recognised after so long an interval,

*M Bthodplogieal Rules 345

think what the general mental capacity of the ants must be !
Fortunately, Lubbock made the matter a subject of experiment.
He took ant larvae from the nest, and did not put them back
again till they v/ere fully developed. The result was, that they
too were quite friendlily received. Plainly, then, there can be no
question of an act of individual recognition. There must be
some characteristic peculiar to all the members of a particular
nest, possibly a specific odour, which determines the in-
stinctive expression of ' friendship.'

It is the same with those facts upon which the conclusion has
been based that ants and other insects that live together in
' states,/ as they are called, possess a fairly well-developed lan-
guage. The animals are undoubtedly able to call in the assist-
ance of others for the accomplishing of tasks too great for their
ow/. strength. But this purpose can be served by quite simple
nvOvements, which are common to very many species of social
/ limals. Since these movements are manifestations of impulse,
hey exert a reflex influence upon the corresponding impulses
of all individuals of the same kind. It is true that action must
in every case be preceded by certain ideational connections.
The ant that finds a load too heavy will connect this impression
of weight with the often repeated perception of its mastery by
united effort, and that again with the idea of assistance by other
ants. But all this is a matter of very obvious association. To
assume a supra-associational intellectual activity for processes
which consist in manifestations of animal instinct of every-day
occurrence, and repeated through countless generations, seems
altogether unjustifiable. It would be entirely contrary to every-
thing that introspection tells us of our own impulsive and
automatic actions.

§n

These considerations lead up to a question which it is important
to raise with regard to the study of animal psychology in
general. We have no other means of estimating the mental
processes of animals than in the light of those of our own con-
sciousness. We must employ these in such a way as to gain
the best and surest knowledge possible of the animal mind.

346 Lectures on Human and Animal Psychology

How is this to be done ? The current animal psychology does
not trouble itself to give any very careful answer ; indeed, a
general answer is not given by it at all. In any particular case,
however, as we have seen, it selects from the totality of mental
processes the intellectual functions, and explains the mental life
of animals in terms of them. Its implicit principle, that is, is
precisely the opposite of the approved maxim of the exact
natural sciences that we should always have recourse to the
simplest explanation possible. It attempts to derive all the facts
of its objective observation from the most complicated mental
processes of human subjective experience. Where there are two
alternatives,— derivation from logical reflection and explanation
in terms of simple association, — it invariably chooses the former.
And the fact that logical reflection is everywhere a possible
explanation is taken as sufficient proof that it is the right one.
But there are two reasons why this particular inference from
effect to cause is not permissible. In the first place, mental
activities are so complex and multifarious, that practically every
objective action is capable of more than one interpretation ;
and it needs very careful consideration of all the secondary cir-
cumstances to decide the actual psychological conditions of a
given result Secondly, logical reflection, just because every-
thing can be subsumed to it subjectively, may itself be trans-
lated into the objective condition of anything. So that the
psychologist who interprets a fact of consciousness as a logical
reflection, when it is not so given, is acting in principle as a
student of natural science wpuld who ascribed the properties
of certain natural objects to the usefulness which they happened
to possess for ourselves or for other organisms. But since
logical reflection is itself a mental process, and may therefore
take its place with other processes as a possible cause of some
psychical effect, the danger of the error becomes much
greater, and the proof of it much more difficult. All the more
reason is there to emphasise the necessity, when we are attempt-
ing a psychological explanation of phenomena which can only be
inferred from their objective results, of always inquiring for
those special characteristics which are of determining value for
ne mode of explanation as compared with another.

Acts of Cognition and Recognition among Animals 347

§ HI

If, with this in mind, we ask : what are the most simple mani-
festations of animal life which cannot be explained without the
introduction of the mental factor ? we come first of all upon
voluntary actions, referable to acts of cognition and recognition.
You see at once that the very names employed to denote these
simplest ideational connections show traces of the fatal
tendency to dissolve all the facts of consciousness in the medium
of logical reflection. That the processes in question consist of
nothing more than simple associations was shown when we
were analysing the corresponding phenomena of the human
consciousness. We used the word ' cognition ' because there was
no other term current to denote the process ; but it is sufficiently
plain from the language of our description that any idea of an
act of logical cognition was very far from our minds. Now
the analogous phenomena of the animal consciousness must, of
course, be treated from' the same psychological standpoint. The
acts of cognition and recognition are processes which represent
the simplest modes of connection between present impressions
and past ideas ; in other words, they are mental phenomena,
which in a large number of cases furnish us with the only
reliable evidence of the existence of a mental life. For to prove
mentality we must be able to prove a persistence of the sense-
impression, — some form of memory, however elementary.
Memory of some kind is presupposed in the cognition of an
impression ; memory of a definite kind, in its recognition. In
the former the impression is assimilated by numerous previous
impressions of the same character ; in the latter it is associated
with a single or with a strictly limited number of past im-
pressions, the terms of the association frequently arranging
themselves in a temporal series.

In the very lowest animals it is only the simple association
process that we term ' cognition ' of an object which plays any
important part ; ' recognitions ' are hardly demonstrable. That
the creature knows its proper food, and may be determined in
its knowledge of it by previous impressions, is regarded as the
first and primal indication of the presence of animal, — i.e., mental
— life, But that an animal recognises a certain object, — e.g., the

Lectures on Human and Animal Psychology

place where it finds its food, — presupposes a separation and
differentiation of ideas which in all probability is not realised at
the lowest stages of organic existence. The simple acts of cog-
nition develope from the primitive animal impulses which are
at the root of the earliest manifestations of life that can be called
psychophysically definite. The origin of the selection of food,
for instance, can only be explained on the assumption that
inherited organisation determines the correlation of pleasurably
toned sensations with certain sense-impressions, and that these
sensations are connected with the movements subserving nutri-
tion. The fact, often confirmed by experiment, that even the
protozoa congregate in light of one quality and avoid spots
illuminated by that of another, must depend upon some such
original sensation-character. The discrimination is made in
terms of sensation and the affective tone attaching to it, as in all
the higher animals. Ants try to escape from a violet light,
but crowd together on a blue surface. Lizards and blind-worms
avoid blue and all the more refrangible colours, but are fond of
red. Again, there may be connected with these instinctive
manifestations of mental life others which indicate an intensifi-
cation of the original affective distinctions by previous impres-
sions. The more frequently experiments are repeated with the
different Kiumination of different portions of space, the more
quickly and certainly does the animal decide for its favourite
colour. And the fact that all animals prefer colours and bright-
nesses corresponding to those of the medium in which they live,
— the winged insects, e.g., blue or white, — may be referred to the
influence of previous impressions. At the same time it is not
improbable that these psychophysical influences have in the
course of generations modified the sensitive elements of the
sense-organs ; so that the affective quality which determines the
preference or avoidance of certain stimuli is so far connate that
it connects at once with the sense-impressions. Thus the exci-
tability of the eye of the owl and eagle is entirely different from
the very first. Nevertheless, there is every reason to suppose
that this difference has been developed in the course of generic
evolution, simultaneously with the differentiation in mode of life
and habit. And the relation of animals to their proper food-
supply is an altogether analogous case. The actions prompted

Acts of Cognition and Recognition among Animals 349

by the nutritive impulse will be first excited by the affective
colouring of certain definite sensations. But when the enjoy-
ment of food has been once experienced, the new and the old
impression become associated. We therefore find that in all
animals the discovery and right discrimination of food-stuffs
are perfected in the experience of the individual life This
'experience,' psychologically analysed, consists wholly in simple
acts of 'cognition,' i.e., in the assimilative effect which previous
impressions have upon new ones of the same character.

It is generally more difficult to say whether an act of
recognition has taken place in a given instance. In recognition
a perception is apprehended as agreeing either with a previous
perception referring to some individual object, or with a strictly
limited group of such previous perceptions. The process ob-
viously presupposes a more highly developed discrimination of
ideas, i.e., a greater store of determinate associations. Often
enough actions of the lower animals which are interpreted as
recognitions belong to the sphere of indefinite cognitions. A
good instance of this is the ant experiment quoted above. The
insect returned to its nest by Pierre Huber, after a separation
of four months, was really known not as an individual, but in
virtue of some generic or family characteristic. This does not,
of course, mean that individual recognition is not possible
among the same insects, though it would probably only extend
over a much shorter time. The ant which brings up its com-
panions to assist it in carrying a load must, naturally, recognise
the object to be carried and the road it has passed over, —
possibly also some of the helping ants. It is well known that
in the higher animals the memory is able to retain particular
facts and objects for a comparatively long period. The dog
recognises its master after an absence of months ; the domestic
cat is thoroughly familiar with the rooms of the house in which
it is kept, and at once makes itself at home after quite a long
absence. The dog, the elephant, and many other animals have
an accurate memory for any previously unknown individual
who teases or. strikes them, and show it by very evident tokens
of displeasure. When it is assisted by instinct and specific
sense-development, this faculty of recognition among the
animals may far exceed that of man in its own particular

35° Lectures on Human and Animal Psychology

sphere. The dog can find its way over a long and complicated
road by means of smell ; the carrier pigeon recognises the
direction in which it flew some long time previously, thanks to
its trained space-memory and far-reaching vision. All these
phenomena, which have sometimes been referred to a mysterious
' sense of locality,' are explicable as dependent upon recollec-
tion, highly developed in one particular direction and assisted
by sense-peculiarities. The carrier pigeon taken from its home
in a closed cage to some unknown and remote spot will either
not return at all, or only by a long and roundabout way.

§ IV

Wherever recognition is possible, other associations may
also be observed. The animal, like ourselves, naturally
associates the similar and the contiguous in time and space.
And we frequently find in the lower animals what we have
observed in man, — that associations give rise to actions whose
result is equivalent to that due to the operation of the in-
tellectual functions. It is here, therefore, in the various forms
of successive association proper, that the act of interpretation
which resolves the mental life of animals into concepts, judg-
ments, and inferences, according to all the rules of logic, finds
freest play. But if the whole body of reliable observation is
carefully tested, and due regard paid to the lex parsimonies,
which only allows recourse to be had to complex principles of
explanation when the simpler ones have proved inadequate, it
seems that the entire intellectual life of animals can be ac-
counted for on the simple laws of association. Nowhere do we
find the characteristic marks of a true reflection, of any active
functioning of imagination or understanding. In saying this,
we are, of course, regarding only well-authenticated facts, and
not those ' travellers' tales ' of which animal psychology has as
many as it has wrong explanations of actual observation. You
may remember the story in Pliny's Natural History of the ele-
phant who was punished during a performance for his bad
dancing, and who secretly set to work to practise in the
night, so as to do better the next time. We may be pretty
•confident in supposing that this tale and many others like it,

Association among the Lower Animals 351

which are still current in the animal psychologies, are either
pleasant inventions or, if they contain a grain .of real observa-
tion, have received so much imaginative embellishment, that its
discovery is practically impossible.

As a matter of fact, the mental life of animals is rich enough
to be able to do without all this. The life of the more highly
organised invertebrates, — even apart from the phenomena con-
nected with the social instincts, to which we shall return later, —
has many features which would astonish an observer untrained
in psychological analysis. Instead of giving you a whole
number of illustrations which are all variations of the same
theme, I will narrate an observation of my own. I remember
it very distinctly, because it was the first time that I had
brought home to me the mental life of a lower animal. I had
made myself, as a boy, a fly-trap, like a pigeon-cote. The flies
were attracted by scattered sugar, and caught as soon as they
had entered the cage. Behind the trap was a second box,
separated from it by a sliding-door, which could be opened or
shut at pleasure. In this I had put a large garden spider. Cage
and box were provided with glass windows on the top, so that
I could quite well observe anything that was going on inside.
At first nothing particular happened. When some flies had
been caught, and the slide was drawn out, the spider, of course,
rushed upon her prey and devoured them, leaving only the legs,
head, and wings. That went on for some time. The spider
was sometimes let into the cage, sometimes confined to her own
box. But one day I made a notable discovery. During an
absence the slide had been accidentally left open for some
little while. When I came to shut it, I found that there was
an unusual resistance. As I looked more closely, I saw that
the spider had drawn a large number of thick threads directly
under the lifted door, and that these were preventing my closing
it, as though they had been so many cords tied across it.

What was going on in the spider's mind before she took this
step towards self-preservation — a step, mark you, which but for
the vis major of the boy-master would have been perfectly
adequate to effect the desired result ? The animal psychologist
will possibly say : ' the spider must first of all have come to
understand the mechanism of the sliding-door, and must have

35 2 Lectures on Human and Animal Psychology

said to herself that a force operating in a definite direction cculd
be compensated, by another in the opposite direction. Then
she set to work, relying upon the perfectly correct inference
that if she could only make movement of the door impossible,
she would always have access to the victims of her murderous
desires. There you have a consideration of general issues, an
accurate prevision, and a cautious balancing of cause and effect,
end and means.' Well, I am rather inclined to explain the
matter otherwise. I imagine that as the days went by there
had been formed in the mind of the spider a determinate asso-
ciation on the one hand between free entry into the cage and
the pleasurable feeling attending satisfaction .of the nutritive
instinct, and on the other between the closed slide and the
unpleasant feeling of hunger and inhibited impulse. Now in
her free life the spider had always employed her web in the
service of the nutritive impulse. Associations had therefore
grown up between the definite positions of her web and definite
peculiarities of the objects to which it was attached- AS well as
changes which it produced in the positions of certain of these
objects, — leaves, small twigs, etc. The impression of the falling
slide, that is, called up by association the idea of other objects
similarly moved which had been held in their places by threads
properly spun ; and finally there were connected with this
association the other two of pleasure and raising, unpleasantness
and closing, of the door. That was surely enough to rouse the
prisoner to action. Any other intellectual or inventive activity
is entirely unnecessary. If she had not had these associations
at her disposal, she would certainly never have hit upon the
plan she did.

LECTURE XXIV

§ I. MENTALITY OF THE HIGHER ANIMALS. § II. ANIMAL PLAY.
§ III. ALLEGED FORMATIONS OF JUDGMENTS AND CONCEPTS.
§ IV. GENERAL SIGNIFICANCE OF ASSOCIATION. § V. MAN ANI>
THE ANIMALS.

THERE seems at first sight to be a very considerable differ-
ence between the expressions of mentality in the higher
animals, more especially the more highly developed do-
mestic animals, and the simple or complex associations which
we ascribed in the previous lecture to certain of the invertebrates,
such as spiders, ants, and other insects with very definite instincts.
The perpetual intercourse of the domestic animals with man
seems to bring them quite near to him on the mental side ; he
exerts a determining influence upon the contents of their ideas,
the direction of their associations, and their whole affective life.
The dog shares the joys and sorrows of its master ; it reads
anger, happiness, or despondency in his face. The trained
poodle is made as happy as can be by its master's praises, and
shows every sign of pride when entrusted with certain duties, as
the carrying of a basket or a walking-stick. Now it is true
enough that all this points to a great diversity of feeling and a
considerable adaptability to the feelings of others. But the
emotions expressed never belong to the sphere of intellectual
feeling, — logical, aesthetical, etc. So that the only certain
inference from the actions in which the animal appears to
resemble man so closely is that it is endowed with a very active
associational mechanism.

There can be no doubt that the behaviour of our more highly
developed domestic animals indicates this activity of association.
As soon as you have taken your hat and stick, your dog knows
that you are going out, and shows by tokens of pleasure and

353 A A

354 Lectures on Human and Animal Psychology

other unmistakable gestures that it wishes to go with you. A
poodle of my own used to be subjected to a thorough washing
every Saturday, and disliked it very much. Various prepara-
tions that were going on in the house would remind him that
Saturday had come ; and he not infrequently disappeared early
in the morning, and only returned late in the evening, when all
fear of the cold water was over. On these occasions he usually
spent the day on the square in front of the house, looking
longingly up at the windows and obviously divided between the
wish to return, and aversion to the fate that awaited him. He
was all the happier when Sunday morning arrived. On that
day my brother, who was living in a neighbouring town, was
accustomed to come over and see me. The dog was more
attached to him than to any of the inmates of the house. He
never failed to keep watch behind the front door from the very
first thing in the morning, welcoming approaching footsteps
with a hopeful wag of his tail, and dropping his head de-
spondently if they disappointed him. At last, when my brother
really appeared, he was greeted with every manifestation of the
most extreme joy. Experiences of this kind not only show that
the mechanical operation of association may extend over a
considerable time, as is proved by the recognition of an indi-
vidual after a number of days, but also, — and it is this which
distinguishes the present instance from a case of simple recog-
nition,— that an animal is itself able to associate events which
coincide in space or time, and to extend these associations over
a relatively long period. The poodle knew, of course, that it
was Saturday simply by the special preparations for cleaning
the house. With that idea was inseparably associated the very
unpleasant idea of his own washing. This association was not
only strong enough to keep him away from the house for the
whole day, but was further connected with the other and far
more complicated association of the following day and the
arrival of my brother. Of course, the regularity of the visits
furthered the formation of the association. At the same time,
we have here a development of temporal ideation reaching
far beyond the connection of directly simultaneous or successive
events It would be utterly wrong, though quite in the manner
of current animal psychology, to make the dog reason in this

Mentality of the Higher Animals 355

way : ' Yesterday was house-cleaning and washing-day ; my
friend usually arrives on the day after that ; therefore he will
come to-day.' The simpler, and therefore the only justifiable,
explanation is, that the experience of previous weeks had made
the succession of these events a stable contiguity-association in
the animal's mind ; and that its expectation of my brother's
arrival after the preceding occurrences was of the same kind as
its expectation that it would get something to eat after the
filling of its platter. The only difference between the two cases
is that the former association extended over a longer time and
embraced a greater number of events than the latter.

A whole host of observations, which are usually interpreted in
terms of intelligent action in the strict sense of the word, are
more or less like these examples of my own. I will only cite
the following, which I take from Romanes' book on Animal
Intelligence (p. 418). The servants of a house had been accus-
tomed during a frost to throw the crumbs remaining from the
breakfast-table to the birds. A cat took advantage of this, and
now and again obtained a hearty meal from one or two of
the assembled guests. The practice of feeding the birds was
therefore discontinued. The cat, however, scattered crumbs on
the grass itself with the obvious intention of enticing them.
Romanes supplements this by another story, in which crumbs
were sprinkled on the garden-walk, and the cat lay in ambush
to catch the sparrows. In this case, however, the cat used to
conceal itself from the walk in a neighbouring shrubbery, and
there await the coming of the birds. But the sparrows showed
themselves more wide-awake than the cat : they waited on a
Avail, never venturing to fly down till their enemy wearied and
went away. Romanes credits the two cats with the same form
of inference. In the latter case the animal reasoned : ' crumbs
attract birds ; therefore I will wait for birds when crumbs are
scattered.' The first cat proceeded a stage further : ' therefore
I will scatter crumbs to attract birds.' There can be no doubt
that the two cases are analogous, and that the simpler is alto-
gether a matter of ordinary association of the sort which is
constantly directing animal action. But there can be no doubt
either that the cat did not make the author's inference. When
•once the association between scattering crumbs and attracting

356 Lectures on Human and Animal Psychology

birds had been formed, the feeling of expectation was sufficient
to cause it to lie in wait for prey as it was accustomed to do in
other cases. This association was precisely like that which the
sparrows had formed, even in its effect upon the will ; except
that the cat was led to undertake a particular action, and the
sparrows to refrain from it. We must admit that the case is
somewhat different when the cat itself scatters crumbs. The
tale is so unlikely, in view of what we know of the general
behaviour of the animal, that we may possibly refer it to self-
deception on the part of the observer, or conjecture that some
chance incident has been wrongly interpreted. The same story
told of monkeys would sound more probable, on account of the
high development of the imitative impulse in those animals.
There is nothing to take the place of this in the cat except the
carnivorous instinct to secure prey. But even if we grant the
correctness of the observation, the action might be explained
by associative processes. The stable association of scattering
crumbs and attracting birds, taken together with the impulse to
catch them, might have enabled the cat to supply one term of
the association-series for itself. But if we leave out this element
of spontaneous activity connected with the specific carnivorous
instinct, we see that the range of association in the cases cited
is not nearly so great as in the above-quoted recollection and
recognition by my dog.

That the action of animals may be determined by memorial
ideas, as well as by the corresponding sense-impressions, can be
very readily shown. I often made the following amusing ex-
periment with my own poodle. I had taught him to spring over
a stick which I held out at the word ' Jump!' One day I called
the word out to him without presenting the stick. At first he
looked at me in surprise, and then, as I repeated the command,
barked impatiently. At last, after I had given the order several
times with a stern face, he decided to make a spring into the
air, but barked loudly at me afterwards, as though to complain
of the absolute absurdity of my command. When I had re-
peated the experiment a number of times, the animal came to
respond at once by springing into the air, but never failed to
protest by growling and barking. The word of command
aroused the memorial idea, and this was sufficient to arouse the

Animal Play 357

action produced by the actual presentation of the stick ; while
the feeling of contrast between idea and object, and of the pur-
poselessness of the act gave rise to unpleasurable emotions
conflicting with the dog's habitual obedience.

§n

The criterion of ' intelligent ' associative action and of in-
telligent action proper can only be this, — that the effect of
association does not go beyond the connection of particular
ideas, whether directly excited by sense-impressions or only
reproduced by them ; while intellectual activity in the narrower
sense of the word presupposes a demonstrable formation of
concepts, judgments, and inferences, or an activity of the
constructive imagination. If . Pliny's story of the elephant
practising dancing by moonlight were true, it would undoubtedly
be a case of imaginative activity in this sense. On the other
hand, the jumping of the dog over an imaginary stick at the
word of command implies memory, but not imagination ; i.e., it
depends not upon the spontaneous arousal of associations, but
upon their discharge by external impressions.

The play of man and the animals differs in the same way as
their ' intelligence.' We regard certain actions of the higher
animals as playful when they take the form of imitations of
purposive voluntary actions. We know that they are imitations
because the end pursued is only a fictitious end, — the real end
being excitation of joyous emotions similar to those which
follow as secondary effects from genuine purposive action.
That means, you see, that the play of animals is for all practical
purposes identical with play among mankind. Our own play,
at least in its simpler forms, — e.g., in the play of children, — is
merely an imitation of the actions of every-day life stripped of
its original purpose, and resulting in pleasurable emotion. The
play of animals bears the same relation to the play of man as
animal life does to human life. The impossibility of transcend-
ing a certain circle of ready-made associations characterises
the play of animals (even of the most highly developed), as it
characterises their mental life in general. Over against the
countless varieties of the play of children, reflecting all con-

358 Lectures on Hitman and Animal Psychology

ceivable relations of life, stands the single form of mock fighting
among the animals. (Trained animals do not, of course, concern
us ; their performances are not real play.) Dogs, cats, and
monkeys, even when they are playing with their young, show
their affection by pretending to fight with them. And though
it is true that play is an indication of high mental development,
and brings the animal nearer to ourselves than any other activity,
it is rather the fact that it plays than the nature of the play
itself which is the important point. Only those animals can
play which reproduce in memory pleasurable experiences, and
are able to modify them so that only their pleasant side comes
to consciousness, and their unpleasant aspect disappears. At
the same time, any comparatively complex associative and
affective activity in the mind of an animal is a sufficient reason
for the origination of playful actions. Animal play never shows
any inventiveness, any regular arid orderly working out of some
general idea. And only where this is found can play be re-
garded as the expression of really imaginative activity. The
simple .and original play of the animals is, if the expression may
be allowed, a purely associational play. When a dog sees
another dog, it does not necessarily feel any hostility towards
it, but still has an inclination to exercise its strength in a mock
fight, and so to gain the pleasure which it has experienced in
real ones. If it obeys this impulse while its mood is friendly,
or at least not hostile, the result is a mutual trial of strength in
a playful contest ; ending often enough, as you have probably
observed in dogs and monkeys, in the arousal of the real joy
of battle and a fight in bitter earnest. In many animals, how-
ever, and especially in those which, like the dog, have been
domesticated for a long time, the inherited instinct appears in
a moderated form from the first ; the connate fighting impulse
seems to become a connate impulse to play.

§ HI

We must conclude, then, that those animal actions which
remind us most forcibly of imaginative activity do not show
any of the specific characteristics which distinguish imagination
from memory. There is no purposive and comprehensive con-

Alleged Formations of Judgments and Concepts 359

nection of ideas, none of the inventiveness which that implies.
In the same way the animal actions which border most closely
on the realm of human understanding give us no warrant for
inferring the existence of true concepts, judgments, and in-
ferences. That writers upon animal psychology have so often
asserted the contrary is due to the interpretation of compara-
tively simple associative processes as apperceptive intellectual
operations.

Romanes gives an account of a series of tests of the intelli-
gence of an elephant sent him by one of his correspondents (p.
401). The story goes to show that 'elephants possess abstract
ideas.' Even if we do not give the phrase ' abstract ideas ' its
philosophical meaning, but simply understand by it general
experiential concepts, we must still admit that the facts recorded
do not prove their existence, but merely indicate a fairly
highly developed associational activity. An elephant was
made to lift various objects with its trunk, — bundles of clothes ;
tree-trunks ; heavy pieces of metal. It was noticed that the
animal gradually ' took in a knowledge of the nature of the
things it was required to lift ' ; light objects were thrown up
easily and quickly, heavy ones slowly and with obvious muscular
preparation, cutting instruments with a certain degree of caution.
The observer concludes ' that elephants recognise such qualities
as hardness, sharpness, and weight.' You will probably agree
that nothing more is necessary for such actions than the for-
mation of definite associations between the visual impressions
of an object and its tactual properties. Such associations
would in any case have been necessary to produce the observed
result, even though the elephant really possessed the general
concepts of light, heavy, cutting, etc. But if once the associa-
tions were formed, they would be altogether sufficient to
determine the ' intelligent ' lifting of such objects, and there
would be no need at all of the further formation of general
concepts.

I spent a great deal of time in trying to discover some cer-
tain indication in various actions of my own poodle of the
presence or absence of general experiential concepts. I was
never able to demonstrate them ; but I made many observations
which rendered its nower to form them exceedingly improbable.

360 Lectures on Human and Animal Psychology

I taught the dog to close an open door in the usual way by-
pressing with the fore feet when the command ' Shut the door! '
was given. He learned the trick first of all on a particular door
in my study. One day I wished him to repeat it on another
door in the same room ; but he looked at me in astonishment
and did nothing. It was with considerable trouble that I per-
suaded him to repeat his trick under the altered circumstances.
But after that he obeyed the word of command without hesi-
tation at any other door which was at all like these two. It is
obvious that when the animal had learned the trick of closing
the door for the first time he had formed no general concept of
' door ' ; otherwise he would have found no difficulty in shutting
others. His action plainly depended upon a quite individual
association. Some force had to be used to form this, as is
always the case with such performances. I stood the dog up
on his hind legs against the open door, while I gave the word of
command, until he responded to the order by voluntary move-
ment. But you will say : might not the further step necessary
to the formation of a concept have been taken when the
animal learned to close the second door? After that he was
able to close others for which he had not been specially trained.
I do not believe that the assumption of the formation of a
concept is necessary even here. It is evident that when the
association between word of command, movement, and closing
of the door had been formed at several doors the more special
association between the particular door and the action of closure
must have become obscured. The association of particular ideas
had developed into a true similarity-association. There is not
the slightest indication of the presence in the dog's mind of the
principal characteristic of the formation of concepts, — the con-
sciousness that the particular object vicariously represents a
whole category of objects. It had throughout only a very con-
fused idea of the ' nature ' of a door. When I ordered it to
shut a door which opened from the outside, it made just the
same movement, — opened the door, that is, instead of closing, —
and though I impatiently repeated the command, it could not
be brought to do anything else, although it was obviously very
unhappy at the ill-success of its efforts. Only after I had on
several occasions let it out of the room, and made it shut the

Alleged Formations of Judgments and Concepts 361

door from outside, did the inability to close it from inside
decide it to go out and repeat the attempt from the other side ;
and then it would at once begin to scratch at the closed door
to beg for readmission.

What holds of concepts holds equally of the alleged judg-
ments and inferences of our more intelligent domestic animals ;
on closer consideration they may be all resolved into obvious
associations, and they fail at the point where the sphere of ex-
ternally suggested association touches that of intellection proper.
I used to take my poodle on summer evenings into a garden
lying across a stream, to which we had access by boat. The
banks were very crowded, and boats were always plying to and
fro. One day the poodle had stayed behind with some other
dogs, and came to the bank too late, so that the boat was at
some distance from the shore when he reached it. There was
nothing left for him but to swim the stream ; and since it was
fairly broad, and he had little love for water, that was very un-
pleasant. Some days afterwards the same misadventure befell
him. He ran up and down the bank whining dismally, and
obviously very averse to repeating his bath. At that moment
a boat-load of passengers pushed off; he sprang in and came
dry-footed and extremely happy to the other bank. Hence-
forth he not infrequently crossed in the same way. Now what
was going on in his mind during this particular action ? Did he
think: ' my master has crossed the stream; this boat is also
about to cross: therefore I shall overtake him if I step in ' ? Of
course we car^ translate the animal's action into this chain of
reasoning. Only we are not then dealing with the process in
its mind, but with a logical interpretation of that process. But
are not the interpretation and the process equivalent ? And
since the chain of reasoning would lead to the same result, how
do we know that it did not actually take place in the dog's
consciousness ? This instance is in truth a good illustration of
the fact that the outcome of a logical reflection is not so com-
pletely identical with that of a mere ideational association.
The two processes present characteristic differences which ac-
quire especial significance in cases like this, where we are deter-
mining the nature of internal experiences. If the dog had sprung
at once into a boat lying upon the shore and waiting to take

362 Lectures on Human and Animal Psychology

in passengers, we should still perhaps hardly have been justified
in crediting it with logical reflection ; the association between
the boats and their passage over the stream might have been
formed in its mind through its frequent journeys across. Never-
theless this association would have been considerably more
complicated ; and its inclusion of a number of memorial
elements, in the absence of the corresponding impressions, would,
have brought it very near the intellectual operations. But it
never occurred to the animal to enter an empty boat and wait.
Not till the boat pushed off did it associate this new crossing
with previous journeys. So that the action bears every mark of
a simple association. If on later occasions, — and I am not sure
about this, — the dog did spring into an empty boat, or one just
filling up, we need not refer this action to the sudden birth of
logical reflection, but can explain it as a gradual extension of
the associational series, resulting from practice. Many accounts
of animal intelligence which are given without falsification or
exaggeration in works on animal psychology would, we may be
sure, oftentimes admit of a similar interpretation, if we were
informed of all the stages in the animal's conduct. You could
hardly imagine a better example of intelligence than the action
of a dog which should cross a stream of his own accord with a
number of passengers who were total strangers to him in order
to visit a garden on the other side. And yet the act becomes
simple enough when we can follow its gradual development in.
detail.

§ IV

All these manifestations of animal ' intelligence ' may be
adequately explained as relatively simple associations. When-
ever we are in a position to investigate the nature of the connec-
tion of conscious processes involved, we look in vain for traces
of logical reflection or real imaginative activity. We can now
understand how it is that the animals lack one function which
is characteristic of the intellectual processes, at the same time
that it is their invariable concomitant, — language. Animals can
express emotion ; the more highly developed of them can to a
limited extent give evidence of the connection of ideas with
their emotions. But the expressive movements of animals never

General Significance of Association 363.

show that regular articulation, that reflection in organic struc-
ture of the nature of intellectual ideation, which is characteristic
of language proper. Animals possess certain elements of
language, just as they possess certain elements of consciousness
which might serve as the basis of intellectual function, but they
do not possess language itself. So that the mere absence of
this external mark would justify us in inferring the absence of
those mental functions of which it is the mark. As a rule, it is.
not any physical obstacle, as is so often thought, which prevents
animals from talking. In very many animals the development
of the organs of speech has gone far enough to enable them to
clothe thought in words, if the thought were there to clothe.
The question why the animals do not talk is most correctly
answered in the old way : because they have nothing to say.
Only we must add that certain movements and sounds charac-
teristic of feelings and ideas seem to be the forerunners of
language ; and that animals give signs that in this connection,
as in others, their mental life is the immediate precursor of our
own.

Indeed, the importance of association for the animal conscious-
ness recalls what we have already said of its value for the human
mind. When we began our consideration of the mental life of
animals, we condemned the tendency of animal psychology to
translate every manifestation of ' intelligence ' into an intellectual
operation. The same reproach could be made against certain
more or less popular views of our own mentality. The old
metaphysical prejudice that man 'always thinks' has not yet
entirely disappeared. I myself am inclined to hold that man
really thinks very little and very seldom. Many an action which
looks like a manifestation of intelligence most surely originates
in association. Besides this, man is constantly translating acts
of logical thought back again into customary associations, and
so increasing the sphere and the intellectual consequences of the
associational processes. By practice we can reduce anything to
association. Trains of thought which at first involved consider-
able intellectual labour are completed with increasing certainty
and mechanical facility the oftener they are repeated. We can
hardly overestimate the facilitation of logical operation and con-
structive imagination which this tendency brings with it. All

.364 Lectures on Human and Animal Psychology

the work spared by associative practice can be employed in new
intellectual achievements. For this reason, thought proper is
continually engaged with permanent mental associations at the
-same time that it is making new ideational connections. It is
a process compounded of logical and associative connections of
"ideas. We may rightly give the name of thought to a train of
ideas whose associations are manipulated by the attention for
•definite intellectual ends, and are only allowed to have weight
within the bounds set by those ends. The best confirmation of
this is given by the expression of thought in language. Though
the general content of the expression is the result of an intellec-
tual process, still the ready-made thought-forms furnished by
•association play no small part in the whole process.

The fruitfulness of this interaction of association and intellec-
tion helps us to understand how it is that many psychologists,
so far from translating all mental activity into logical reflection,
prefer, on the contrary, to regard thought and imagination as
forms of association. We saw earlier that there are external
and internal characteristics which clearly differentiate these
processes. The associationist psychology can give no account
of them. It ignores them, identifying imagination with memory
-and referring logical thought to logic as distinct from psycho-
logy, as though the forms discovered by logic must not in the
last resort rest upon psychological facts and laws. According
to this school, the creations of imagination and intellect keep
even pace with the activity of association. Dreaming and
mental disturbance furnish, of course, a direct refutation of such
a view; but the associationist theory makes light of that. It
pays so little regard to the laws of ideation that it does not need
to spend any time in considering exceptions.

§V

In spite of these essential differences between the intellectual
processes and pure associations, there is an intimate correlation
and mutual furtherance of the two in our own consciousness.
That is possible simply because they are both stages in the
same development. The duty of association is to form those
-.multifarious connections among the conscious elements which

Man and the Animals 365,

enable us to comprehend a whole number of previous experiences
into a resultant mental force, such as that which is employed in
each separate act of voluntary attention, and on the basis of
which the activity of association may be directed to the achieve-
ment of definite intellectual ends. So that intelligence springs
from association, and then turns round again to enrich it by new
connections which will facilitate the employment of thought in
the future.

It is this relation between association and intelligence which
must decide our answer to the final question which arises out
of our investigation of the intellectual capacities of animals : are
we to think that the gulf which separates the animals from man,
which is on its mental side the gulf between association and
intelligence, can ever be bridged ?

In view of the facts of individual human development, we can
hardly do anything else than reply with an unconditioned affir-
mative. The boundary line between the purely associative pro-
cesses which simulate intelligence and really intellectual actions
may be crossed, because in actual fact it is crossed in the life-
history of every one of us. From the stock of associations
which we begin to lay in from our earliest childhood, there
gradually developes the collective mental force of the individual
personality, which manifests itself in self-consciousness, in active
attention, and in voluntary control of ideation. And in this last
especially we can clearly trace the influence of the increasing
store of stable associations and the corresponding enrichment
of affective and conative mentality which comes with it.

But in its application to the relation of man to the animals
our question falls into two special inquiries : is it probable
that species or individuals of animals existing to-day will ever
cross the boundary line ? and is it probable that man himself
at some period of his development bridged the gulf which to-day
separates him from the animals ?

The first of these questions may be as certainly answered in
the negative as the latter may in the affirmative. The step
from association to intelligence proper is undoubtedly the
longest ever taken in the course of mental evolution. When
once the mind has reached the level of logical thought and con-
structive imagination, it has before it that prospect of unlimited

366 Lectures on Human and Animal Psychology

advance which must inevitably at some point in time be realised
.in civilisation and history. That any species among the higher
.animals can make this tremendous progress is rendered alto-
gether improbable by the general nature of their psycho-
physical organisation. Besides which this organisation appears
•to be so far determinate that further modification cannot tran-
scend very narrow limits. And perhaps the struggle for existence
in the organic world would prevent any large number of quite
differently constituted beings from rising by their own efforts to
the height of civilisation and historical existence on a single
planet.

It is otherwise with the second question. The laws of physical
development put it beyond all doubt that man passed through
lower forms of life before he reached his present stage of organi-
sation. And the laws of mental development make the same
conclusion at least exceedingly probable. Just as every one in
the course of his own individual development takes the step
from association to that intellectual conscious activity which
arises from it, so must mankind at large have done at some
point in the world's history. It was the first step from savagery
•to civilisation. And surely it is no disparagement of the value
of mental development to regard it as having been from the
beginning what we see it to-day, — an evolution of mind from
itself, proceeding under the conditions set by the environment
in accordance with the universal laws of mental life.

LECTURE XXV

."§ I. CONNECTION OF AFFECTIVE STATES IN CONSCIOUSNESS. § II.
SENSORY ACCOMPANIMENTS OF COMPOUND FEELINGS. §111. EMO-
TION. § IV. INTELLECTUAL FEELINGS.

§ I

OUR original plan in these lectures was to begin with the
examination of particular mental processes, — sensations
and ideas, feelings and voluntary actions, — and then to turn our
attention to the interconnection of all these processes in con-
sciousness. But when we came to analyse complex states of
mind, it seemed better to take their components separately and
examine them as we examined the simpler phenomena of mind,
although their isolation was no more than an abstraction. We
have accordingly spoken in the preceding lectures only of the
ideational side of consciousness. We could not leave feeling
and will altogether out of account, because of their importance
for the apperception and association of ideas But we said
nothing of the relation of feeling and internal voluntary action
to the other affective states of consciousness and to external
voluntary action. We will now glance briefly at the more
complex affective processes.

The sense-substrate of all the more complex affective states
we have found to be the common feeling. Like the particular
sense-feelings which give rise to it, this is either a pleasurable
or an unpleasurable feeling. Indefinite as these categories may
seem, they are characteristic for the mental nature of affective
activity in general. The physical excitations underlying the
sensations to which affection attaches differ only in intensity and
in the nature of the stimulus which arouses them. Sensations
.as such, therefore, present only intensive and qualitative differ-
ences. But when the physical excitation also gives rise to an
•affective process, we find these two polar opposites of pleasure

367

368 Lectures on Human and Animal Psychology

and pain, the principal determinant of which is the intensity of
stimulus. As we intensify any sense-impression, pleasurable
feeling passes gradually into unpleasurable, and that into pain.
While the intensity of the physical excitation increases con-
tinuously, its affective concomitant changes from one quality
into its exact opposite.

At the same time the conditions of this qualitative change are
really present in the physical excitation. The effect of stimula-
tion upon the course of the physiological processes in the
organism must be either favourable or inhibitory. Moderate
stimulation is indispensable for the continuance of normal func-
tion. Organs which are not used for a long time degenerate
morphologically. Stimuli whose intensity is regulated by the
normal capacity of the bodily organs themselves are therefore
most beneficial for the maintenance of life : they call for a uni-
form expenditure of energy which is never pushed to the limit
of exhaustion, but always leaves some small surplus of force in
reserve. These normal internal stimuli also excite feelings of
moderate intensity which unite to form the common feeling of
comfort. When, on the other hand, the intensity of stimulus
becomes so great that the organs are in danger of exhaustion
or of entire destruction, there follows either a general disturbance
or a temporary arrest of the vital mechanism. This excessive
stimulation conditions not only a morphological and physio-
logical derangement of the bodily organs, but also feelings of
unpleasantness or pain.

The reason for these differences in the affective character of
the excitation, — differences of pleasure and pain, — is given,
therefore, with the physical attributes of stimuli and the changes
which they set up in the organs of sense. But the differences
themselves are altogether mental in nature, manifesting them-
selves simply as modifications of the general state of mind.
Though originally produced by sense-stimuli, they contain no
necessary reference to physical processes, so that we may have
feelings which bear the same relation to the simple sense-feelings
as does a train of logical thought to a particular sensation.
Pleasure and pain mean alteration of our general psychical con-
dition. They do not, therefore, require a sense-stimulus for
their origination ; they may be called up by the mere idea of

Connection of Affective States in Consciousness 369

a sense-stimulus or by the intellectual content of a single idea
or an ideational association.

At the same time, the purely mental feelings always rest upon
a sensory substrate ; just as on the intellectual side of mind the
most abstract concept is still so far dependent upon sensation
that it cannot be thought without translation into a vicarious
sense-idea.

This connection with sense can be demonstrated just as plainly
for feeling as it can for idea. Feelings which attach to the most
complicated ideational series have the same names as the simple
organic feelings. ' Pain ' may signify either the excessive excita-
tion of a sense-organ, or the higher degrees of general mental
discomfort We speak of the 'pain' caused by the loss of a
friend, or by the disappointment of our hopes, just as we do of
the ' pain ' of a wound or of a diseased organ. We talk of
' burning ' love, of ' pressing ' care, of ' gnawing ' remorse. In a
word, our names for all kinds of affective states which have no
direct connection with sense-impressions are derived either from
peripheral sensations or from the feelings to which they give
rise.

We may, of course, term this secondary meaning of the words
purely figurative. We speak metaphorically of being ' torn *
by conflicting emotions. So ' agony ' of mind, the ' weight ' of
care, and similar expressions which are used both for bodily and
mental conditions would be metaphors which we easily overlook
because we are always using them and have no others at our
disposal. Nevertheless there must be some psychological reason
for this figurative characterisation of the affective consciousness ;
there must be some sort of relation between the sense-feeling
from which the name is taken and the intellectual feeling to
'vhich it is applied. The most obvious relation would be a
temporal association of the two processes.

The question then arises whether mental pain is associated
with bodily, and whether when pain ' presses ' and remorse
' gnaws ' the sense-feeling of pressure or of gnawing pain is
really present.

B B

370 Lectures on Human and Animal Psychology

If we look closely at the intellectual feelings, especially in their
more intensive stages, we can hardly doubt that they are in-
variably accompanied by sense-feelings. These concomitant
feelings often attain an intensity equal to that of the sense-feel-
ings aroused by direct external or internal stimulation. Some-
times they may be even localised with some degree of
definiteness. They always evince a determinate quality which
varies with the general affective condition, and which is reflected
in the expressions which we employ to describe this. All ex-
cessive feeling is attended by physical pain, whether diffused
over the body generally, or restricted to a particular organ.
Moderate excitations also affect the sense-feelings though less
strongly, and are more definitely localised. References to this
localisation of the sense-stimulus in particular affective states
are found in ancient literature. Every passion was supposed to
be seated in a particular organ ; and it must be admitted that
where observation was wanting imagination took its place.
Anger was placed in the liver, envy in the spleen, the higher
emotions in the organs of the breast. Even to-day the heart is
the seat of the most various affective states. Care and dis-
appointed hope bring on heartache ; despair dies of a broken
heart ; love through all its changes and chances has its source
and centre in the heart, and ' faint heart never won fair lady.'

There is really good reason for this relation of the heart's
activity to the state of feeling ; for the cardiac nerves are those
most easily excited by changes in our affective condition.
Every affective excitation manifests itself in a weaker or
stronger, quicker or slower, heart-beat. Joy and hope make the
pulse quick and strong ; care and anxiety render it weak and
slow ; terror arrests it altogether. And there are many indi-
cations that other organs react to affective changes. It has
often been noticed that violent anger results in a return of the
bile to the blood, which means a derangement of the function of
the liver. The lachrymal glands are very easily excited by the
feeling of sorrow. And we should undoubtedly discover other
similar interrelations were it not that they have no external
symptoms. Besides the particular organ which is especially con-

Emotion 371

cerned in a particular affective state, there are always other organs
more or less affected ; and it is the common feeling resulting
from the sum total of these sensations that constitutes the sense-
substrate of the total affective condition. The muscles, e.g., are
almost always involved in this secondary excitation. We have a
direct measure of the energy and tension, or of the exhaustion
and relaxation of our muscles in sensation of movement ; and our
general affective state is altogether different according as the
limbs are motile and elastic or are heavy loads to weigh the
body down. The feeling of the moment is here of the greatest
importance. A feeling of joy and excitation makes movement
easy and prompt ; a depressing feeling renders it slow and
heavy.

We must try to explain how it is that sense-excitations are
always present in greater or less degree in affective processes.
The view of the ancients that the excited organ is the direct
seat of the feeling cannot, of course, be maintained. We know
quite certainly that the parts of the body most closely related
to mental activity are the central organs of the nervous system.
It is here that the impulse must arise which has the sense-
feeling as one part of its result. The symptoms observable in
the peripheral organs simply indicate that this central excitation
has a different seat at different times, and consequently
produces different organic changes, — now altering the pulse,
now deranging the liver, now affecting the muscular system.
In fact, we have before us a phenomenon which presents a
certain analogy to reflex action : only that its source is not to
be looked for in external stimulation, but in an activity of the
central organs.

These peripheral symptoms are of especial importance, as prov-
ing that there is no complete separation of mental process and
bodily function in the sphere of feeling any more than in that
of ideation, but that the two are intimately interconnected.

§111

The affective processes which attach in consciousness to
ideational connections are generally designated emotions. They
are among the most important mental phenomena, exerting a

372 Lectures on Human and Animal Psychology

marked influence both upon ideation and voluntary action. They
resemble feelings in that they are subjective processes not
directly referred to external objects ; they differ from them in
that they involve change in ideation and reactions in the organs
of movement. Feelings, that is, are not accessible to external
observation, or at least only become so when they pass over into
emotions. Then they are reflected in certain expressive move-
ments. These are further connected with reactions of the heart,
the blood-vessels, the respiratory muscles, and certain secretory
organs, which take on a special characteristic form in each par-
ticular emotion.

This twofold relation of emotion to feeling and ideation has
led to a diversity of view as to its nature. It has been regarded
both as an intensive feeling, and as a feeling originating from the
train of ideas. Neither of these definitions does it full justice.
The typical emotion has three stages : an initial feeling ; a
subsequent change in the train of ideas, intensifying and quali-
tatively modifying the * initial feeling ; and (always supposing
that the emotion is distinct and well defined) a final feeling, of
greater or less duration, which may possibly give rise to a new
emotion of which it forms the initial feeling. The principal
difference between feeling and emotion, that is, consists in the
second stage : the alteration in the train of ideas. The presence
of this alteration enables us to divide emotions into two classes,
excitant and inhibitory. Instances of the former are joy and
anger ; of the latter, terror and fear. At the same time all very
intensive emotions are inhibitory in character, and it is only when
they have run some part of their course that their excitant side
comes to consciousness. On the physical side, the effect of
emotion upon the train of ideas is accurately reflected in ex-
ternal movement. The excitant emotion quickeris ideation, and
involves heightened mimetic and pantomimic movement, increase
of cardiac activity, and dilatation of the blood-vessels ; the in-
hibitory emotion paralyses, or at least relaxes, the muscles, slows
the heart-beat, and contracts the vessels. All these physio-
logical effects havetheir accompaniment of sense-feeling which
intensifies the affective elements in the enaction.

Less intensive degrees of emotion are called moods. It is a
general rule that the duration of emotion varies inversely with

Emotion 373

its intensity ; so that moods are more permanent states of
mind than emotions proper. Violent emotions are sometimes
termed passions. The name indicates that strongly affective
states, which oscillate between the feelings of pleasure and pain,
tend invariably towards the side of the latter. ' Passion ' also
implies that a particular emotion has become habitual. Hence
the word is often used to denote a permanent condition which
finds its expression in frequent outbursts of emotion.

The most indefinite emotions are joy and sorrow. All the
rest may be regarded as forms of one or the other of these two
fundamental moods. When, e.g., sorrow is directed upon the
external object which excites it, we call it care. We can only
be careful about others ; and if we wish to express the fact that
an object arouses no interest in us, we say that we do not ' care '
about it. The subjective opposite of care is melancholy. The
melancholiac is centred in himself; he withdraws from the
world to brood in solitude over his own pain. Care and
melancholy become anxiety and dejection when they pass from
emotions to permanent moods. Intermediate between these
objective and subjective forms of sorrow, stand gloom and
depression. We may be gloomy as to our fate in the world and
depressed about a loss we have suffered, or we may be gloomy
or depressed without any external reason simply because our
mood will have it so.

Joy, like sorrow, assumes different forms according to the
direction which it takes. But we have not nearly so many
words to express joyous emotion as we have to express sorrow.
A joyous mood we call cheerfulness, or in its higher stages
hilarity. But we cannot tabulate the joyous emotions as
objective and subjective, as we could their opposites. It may
be that our poverty of words points to a distinction in the facts
of our affective life. The joyous emotions appear to be more
uniform, less variously coloured, than the sorrowful.

The emotions of joy and sorrow, whether their reference is
mainly external or to the feeling subject, are always subjective
in character ; the affective excitation of our own minds is al-
ways the principal thing. A mood, on the other hand, may be
objectified by our putting our own feelings into the external
objects which excite them. If joy and sorrow are the expressions

374 Lectures on Human and Animal Psychology

of an internal harmony and disharmony, these objective emotions
are the result of some external harmonious or inharmonious
impression. Like and dislike are the most general forms of
objective emotion, corresponding to joy and sorrow on the
subjective side. They further imply a movement to or from the
object ; what we like attracts us : what we dislike repels us. And
this movement finds its expression in the various particular
forms in which the general emotions occur. The attraction
which a pleasing object has for us we call charm ; a thing is
' charming ' which both pleases and attracts us. The opposite of
charm is repulsion, a violent dislike which makes us turn away
from an object in displeasure. Repulsion becomes aversion, and
at a still higher stage anger, when it is turned directly upon the
repellent object ; it becomes chagrin and mortification if the
unpleasant mood can find no outlet. The extreme degree of
anger is rage ; the extreme of mortification is exasperation.
The opposite of chagrin is contentment ; when pleasantly con-
cerned with external objects it becomes delight, when quietly
occupied with its own affairs, happiness.

The two opposite processes of charm and repulsion find a
meeting point in indifference. Indifference has a tendency in
the direction of unpleasantness ; when sense or thought is sated
with the indifferent or perhaps originally attractive object, it
passes over at once into repugnance. Repugnance is as much
sense-feeling as emotion. In the latter shape, it has an objective
form, antipathy, and a subjective, discontentedness. If the
emotion becomes a permanent mood, we have weariness and
dissatisfaction.

In all these cases, emotion and mood are at once distinguish-
able from sense-feeling by their connection with a train of
strongly affective ideas. When we feel joy or sorrow, our mood
is the result of some pleasant or painful experience which may
be resolved into a number of ideas. If we are mourning the
death of a friend, our consciousness is filled by affectionate
memories, more or less clear or distinct, which co-operate to pro-
duce the emotion. If we are made angry by some insolent
remark, our first feeling is one of violent displeasure ; then our
mind is flooded by a torrent of ideas connected with ourselves,
the personality of our assailant, and the more immediate cir-

Emotion 375

cumstances of the insult. Most of them will not attain to any
degree of clearness, but all are held together by the feeling of
displeasure, which in its turn is intensified by the sense-feelings
accompanying our expressive movements.

A simple sense-idea which has no special relation to our past
mental history will, therefore, hardly be able to excite an emo-
tion, though it may call up quite intensive sense-feelings.
Where an emotion appears we may assume the presence of
memorial ideas, of experiences in which a similar sense-impres-
sion was somehow concerned. The full and harmonious tone of
a peal of bells sounds holiday-like to us, because we have been
accustomed from childhood to interpret the chimes as har-
bingers of holidays and religious festivals ; the blare of the
trumpet reminds us of war and arms ; the blast of the horn
brings up the green wood and the tumult of the chase ; the
call of the cuckoo tells us that spring has come ; the chords of
the organ suggest a congregation assembled for devotion.

It is probably memory again which determines our affective
reaction to colour-impressions, although in their case the ideas
aroused are not so clear or distinct. Why is white the colour
of innocence and festivity, black the colour of mourning and
severity ? Why do we choose blood -red to express energy and
spirit, or purple to express dignity and solemnity ? Why do
we call green the colour of hope ? It would be difficult to trace
the mood to its original source in each particular case. In
many cases it probably arises from an obscure association
of the colour with the occasions when custom prescribes
its use. Purple has been the royal colour since time began ;
and black is almost everywhere the colour of the mourner's gar-
ments.

It is true that this association does not fully explain the con-
nection between the sense-impression and the mood which it
arouses. There must be some original reason for the choice of
one particular sense-stimulus, and no other, as the expression
of an affective state. It is perhaps justifiable to look for this
reason in the relationship between the sense-feeling and the
affective character of particular emotions. The sensation as
such could then originally excite only a feeling ; but this might
become emotion as soon as consciousness had at its disposal

376 Lectures on Human and Animal Psychology

affectively efficient memorial ideas, into which the sensation
naturally entered as a normal constituent.

Emotions exhibit peculiar modifications when their affective
character is not determined, as in the cases hitherto considered,
by impressions and ideas belonging to the present and thought
as present ; but by ideas which refer to the futttre, whether in
the way that an occurrence is definitely expected, or that some
indefinite idea of the future gives rise to a feeling, and through
it to an emotion.

The most general of these expectations of the future is ex-
pectation itself. In it we outrun the impressions of the present,
and anticipate those which the future will bring. We look for-
ward to its realisation ; and if this realisation is postponed, it
becomes what we call strained expectation ; the bodily feeling
of strain accompanies the emotion. In expectation the muscles
are tense like those of a runner awaiting the signal for
the race, although very possibly the expected impression de-
mands no motor response whatsoever. Expectation becomes
watching if the expected event may happen at any moment,
and our sensory attention is wide awake to prevent its passing
unnoticed. The tension is relaxed with the appearance of the
expected impression. If the consequent perception fulfils our
expectation, we have the emotion of satisfaction ; if not, that
of disappointment. Satisfaction and disappointment constitute
sudden relaxations of expectant attention. If expectation is
prolonged, its tension will gradually disappear of itself : for, as
you know, every emotion weakens with time.

The opposite of disappointment is surprise. Surprise is the
result of an unexpected event. In it we have ideas suddenly
aroused by external impressions, and interrupting the current
train of thought in a way which we did not anticipate, and
which at the same time strongly attracts our attention. Sur-
prise may be in quality pleasurable, painful, or altogether in-
different. A special form of it is astonishment. Here the event
is not only unexpected at the moment, but unintelligible for
some time afterwards. Astonishment is therefore a kind of
continued surprise. If it passes into a still more permanent
inood, it becomes wonder.

The feeling of rhythm, which is the single psychological

Emotion 377

motive in dancing, and ranks with harmony and disharmony as
a psychological motive in musical composition, contains the
elements both of expectation and satisfaction. The regular
repetition in rhythmical sense-excitation makes us expect every
succeeding stimulation, and the expectation is immediately
followed by satisfaction. Rhythm therefore never involves
strain, or if it does, it is simply bad rhythm. In pleasant
rhythms satisfaction follows expectation as quickly as possible.
Every impression arouses the expectation of another, and at the
same time satisfies the expectation aroused by its predecessor,
whose temporal relations it reproduces. Rhythm, that is, is an
emotion compounded of the emotions of expectation and satis-
faction. A broken rhythm is emotionally identical with disap-
pointment.

Hope and fear may be regarded as special forms of expecta-
tion. Expectation is indefinite. It may refer to a desirable or
undesirable, or pernaps to a relatively indifferent, event. Hope
and fear give definiteness to expectation : hope is the expecta-
tion of a desirable result, fear that of something undesirable.
It is hardly correct to call hope a future joy, and fear a future
sorrow. The feelings can as little penetrate into the future as
the senses. Hope and fear are the expectation of future joy
and future sorrow, but not joy and sorrow themselves. Either
of them may be unrealised, just as expectation may lead to
satisfaction or disappointment.

Fear of some immediate disagreeableness is called alarm.
Fright bears the same relation to alarm as does expectation to
surprise. Fright is the surprise occasioned by some sudden
terrifying occurrence. It • becomes consternation when the
occurrence physically paralyses the individual experiencing it ;
and it is called terror when he stands amazed before the event.
Consternation is therefore the more subjective side of fright, and
terror its objective side. If fear is continued, it becomes un-
easiness. The uneasy mind is always afraid ; every occurrence
alarms it. In other words, the emotion has become permanent,
but at the same time somewhat less intensive.

378 Lectures on Human and Animal Psychology

§ IV

The emotions both of the present and future assume the most
varied forms according as the ideational content of the moment
changes. Especially important are those attaching to certain
intellectual processes and originating in the peculiar feelings
which accompany them. We can distinguish four kinds of
intellectual feelings : the logical, ethical, religious, and aesthetic.
Attaching as they do to very complicated ideational connec-
tions, they almost invariably pass over into emotions, and in that
form exert upon our mental life an influence which far exceeds
that of any other affective process. Their analysis belongs, of
course, to the special sciences from which they take their name.
But we will devote a few words to the logical emotions ; first
because they are often overlooked altogether, and secondly
because their relationship to the emotions of the future enables
us to use them as illustrations of the passage of emotion ia
general into the particular forms of intellectual emotion.

It is well known that the rapidity of the course of thought
exerts a considerable influence upon our general affective con-
dition. It is not indifferent to us whether our ideas succeed
one another at their normal rate, or proceed slowly with many
inhibitions and interruptions, or pour in upon us in perplexing
confusion. Each of these cases may be realised whether from
internal or external causes. Our state of mind at the moment,
the topic of our current thought, and external sense-impressions
may all be of determining influence. The traveller in a new
country is well content when his carriage takes him quickly
from one impression to another, — not so quickly that he cannot
assimilate what he sees, but not so slowly that he is always
wishing himself farther on amid new scenes. He is not so
satisfied if he is lumbering along in a heavy waggon, passing
for days together through the same scenery when he longs to-
be at his journey's end, or is curiously anticipating novel ex-
periences. Nor is he quite happy when the railway takes him
swift as an arrow through a country rich in historical associa-
tion, and he tries in vain with deafened ears and tired eyes to-
fix some of its features in his memory.

This general result can be produced by internal causes just as

Intellectual Feelings 379,

well as by the variation of external impressions. If you have
to solve a mathematical problem in a short time, your thoughts
trip each other up ; you are in a hurry to get on, but are obliged
to go back, because you have been following out a second
thought before you had brought the first to its conclusion. And
it is not less disagreeable to be arrested in the middle of your
task because your thought halts, and you cannot answer the
next question. On the other hand, work becomes a recreation
when one result leads certainly and easily to another.

We have therefore the three emotions of confused, inhibited,,
and unimpeded thought. The two last are closely related to
the emotions of effort and facility. Correlated with these are
the sense-feelings attaching to ease and difficulty of muscular
action. They are generally present to some degree in the
corresponding emotions, even when the causes of these are
wholly mental. The feeling of effort is a weight which presses
upon the affective condition, and whose removal is accompanied
by a sudden feeling of pleasure. This characteristic feeling of
relief affects us mainly by way of contrast to our previous mood.

Special forms of the emotions of unimpeded and inhibited
thought are those of enjoyment and tedium. In enjoyment our
time is so well filled by external or internal stimuli to ideational
activity that we hardly notice its passage, if we do at all. The
nature of tedium is indicated by its name. Our time is unoccu-
pied, and passes slowly because we have nothing else to think
of. Tedium, therefore, has a certain affinity to expectation, but
it is an expectation that has remained indefinite. It does not
expect or anticipate any particular occurrence, but simply waits
for new events of whatever kind they may be. A long con-
tinued expectation always passes into tedium, and an intensive
tedium is hardly distinguishable from strained expectation.

Related to the feelings of effort and facility are those of failure
and success. Investigation and discovery are attended by
feelings which show a close resemblance to those of effort and
facility. The feelings of agreement and contradiction are some-
what different. They originate in the comparison of simul-
taneous ideas, which in the one case are accordant, and in the
other refuse to be connected.

Doubt, which we have already discussed under the heading

380 Lectures on Human and Animal Psychology

of oscillatory feelings (Lecture XIV., p. 219), is not the same as
contradiction. The doubter cannot decide which of two alter-
natives is the correct one ; he is in contradiction with himself.
The conflicting ideas are nothing real, but simply products of
his own thought, so that there is always the possibility that the
contradiction in doubt may be resolved by experience or more
mature consideration ; and so far doubt is related to the emo-
tions of the future. This relationship becomes still more
apparent in a special form of doubt, — the feeling of indecision.
When we are undecided, we are in contradiction with ourselves
as to which of different roads we shall follow, or which of differ-
ent actions we shall choose. Indecision is therefore a doubt
implying reference to action and resolved by it.

LECTURE XXVI

I. EXPRESSION OF THE EMOTIONS. § II. IMPULSIVE AND VOLI-
TIONAL ACTION. § III. INSTINCTIVE ACTION. § IV, THEORIES OF
INSTINCT.

WE have seen that the movement among ideas which is
characteristic of emotion in general is always attended
by physiological movements, which exhibit specific differences
according to the intensity and quality of the particular emotion.
These expressions of the emotions have more than a symptomatic
interest : they are genetically important. It is through them
that we are able to understand the relation of emotion to the
development of external voluntary action. Emotion bears the
same relation to this as feeling does to the internal will-process.
The transition from volition to external voluntary action runs
parallel with that from feeling to emotion. But just as not
every feeling develops into a volition, so emotion need not
necessarily or invariably lead to a voluntary act. To take a
special instance, the control of emotion which is natural to the
morally and intellectually mature consciousness consists for the
most part in its inhibition at the boundary line which separates
it from external voluntary action. In the savage and the animal
any emotion that is at all intensive passes over irresistibly into
action. And even where the inhibition is effective, the internal
tension always finds relief in movements whose only differentia
is that they are not intended to bring about any determinate
result. In this way arise the ' pure ' expressions of emotion,
which are simply symptomatic of a particular internal affective
state. They are rudiments of true voluntary actions.

Among the regular expressions of emotion are the mimetic
movements. They are the most characteristic of any for the
nature of the particular emotion. Physiologically considered,

.382 Lectures on Human and Animal Psychology

they correspond to definite reflex movements in the facial sense-
organs. Thus the mimetic movements of the mouth, which are
so important for the expression of the affective state, resemble
the reflexes set up by the action of taste-stimuli (acid, bitter,
sweet, etc.). When a man ' looks sour,' the lips are drawn out
laterally, so that there is more space between them and the
sides of the tongue, which are especially sensitive to acid. In
the ' bitter ' expression the posterior portions of the tongue and
palate, the parts most sensitive to bitter, are held apart. c Sour '
and ' bitter looks,' i.e., depend on reflex movements which serve
to prevent the contact of certain ill-tasting substances with the
portions of the organ most sensitive to them. With the ' sweet '
expression it is just the reverse. The tip of the tongue is the
part most sensitive to sweet. The expression consists in a
sucking movement, calculated to bring the tip of the tongue
into as complete contact as possible with the sweet substance.
We may imagine that all these movements depend upon a
uniform connection of certain nerve- fibres and nerve-cells, the
reflex movement being gradually restricted^ by that process of
regulation which we discussejd abov£ (Lecture VIH., p 128).
Direct evidence for this latter supposition is furnished by the
fact that in early life the mimetic movements are more diffuse
and indefinite than they become later on ; the movements of the
mouth, e.g., are invariably accompanied by general facial con-
tortions, and often by movements of other parts of the body.

But the mimetic movements appear not only as the response
to special sense-stimuli, for which they are teleological reflexes,
but also as the expression of internal emotion. Unpleasant
excitations, of whatever kind, will manifest themselves in ' sour '
and ' bitter ' looks. The ' bitter ' expression varies with the
different degrees of contempt, abhorrence, and loathing ; the
4 sour,' which culminates in weeping, may denote mental as
well as physical pain and affective disturbance. So that the
facial expression becomes symbolic, so to say ; it is the sensible
index of a mental condition. This assumes, of course, that the
sensible expression and the sense-excitation producing it are
more or less closely related to the emotion. And that is the
case. All emotions, you remember, are accompanied by sense-
feelings, though these may only become clearly perceptible

Expression of the Emotions 383

when the emotion is very intensive. Now these mimetic move-
ments mean movement-sensations from the muscles, and they
in turn give rise to sense-feelings which call up clearly enough
the peripherally excited sensations to which they correspond.
When we are looking ' sour ' or ' bitter ' or ' sweet,' we think
that we are actually tasting some acid or bitter or sweet sub-
stance ; because whenever these stimuli affect us the reflex
movement follows, and so the sensation of the mimetic move-
ment is fused with the sensation of taste proper.

The process by which these movements develope, then, will
be somewhat as follows. Every affective excitation is attended
by bodily movements. Some of these gradually obtain an
advantage over the rest, those, i.e., whose affective tone is
similar to that of the emotion. This is a process of restriction
of movement, completely analogous to that of the gradual
restriction of reflex movement discussed above. It is true that
the mimetic movements and the sense-feelings attaching to
them are few in number as compared with the infinite diversity
of emotion and mood. They can do no more than indicate the
general class to which a particular affective state belongs. Still
they admit of a certain amount of variation, as different facial
expressions are combined or modified in detail. But the mimicry
becomes more and more indefinite and equivocal as the
emotion grows more intensive.

Those mimetic movements which serve as a means for the
expression of emotion and mood cannot obviously be regarded
as true reflexes, whose invariable antecedent is the operation of
sense-stimuli. They may with better right be termed impulsive
movements, if we understand by ' impulse' the effort of con-
sciousness to induce the physical condition appropriate to a given
psychical condition. The reflex need not involve any conscious
process at all ; in impulse some such process appears as a
necessary condition, either antecedent to the external movement,
or at least simultaneous with it. Do not misunderstand the
ascription of a symbolic meaning to impulsive movements as
compared with the same mimetic movements in their purely
reflex function. We do not mean that they once were simply
reflexes, and that the symbolic meaning has gradually been
developed from their former significance. Observation decisively

384 Lectures on Human and Animal Psychology

negatives any such view. We have, on the contrary, every
reason to suppose that the movements were first impulsive and
later became reflex. The new-born child, which has never tasted
acid or bitter or sweet, makes the corresponding mimetic move-
ments quite unmistakably. When it cries, the ' sour ' and
' bitter ' expressions appear, alternately or in combination.
Before its lips have ever closed on its mother's breast, it makes
sucking movements, and so 'looks sweet.' In the course of
some weeks there develops the mimetic movement of laughing,
the index of pleasurable mental excitation.

These phenomena indicate quite clearly that the human child
when it first comes into the world possesses feelings and
emotions ; and that even at this early stage of life the emotions
find expression in movements whose affective character is
related to that of the emotions themselves. There is pre-
supposed either a previous mental development, or a connate
adaptation of bodily movement to mental state. There has
obviously been no such development in the course of the indi-
vidual life. We must, therefore, assume a connection which for
the individual is original, i.e., connate.

How is this to be explained ? The most obvious thing to do
is to derive the association from the organic interconnection of
nerve-fibres and nerve- cells. We may assume that the great
majority of the sensing organs are intimately connected within
the central nervous system with the motor fibres running to the
mimetic muscles. But there is always the possibility that these
connections are further developed in the course of the individual
life ; movements which at first were diffuse and indefinite
gradually becoming restricted. And observation raises the
possibility to certainty : we find a continuous and continually
increasing restriction of the mimetic movements. At the same
time, we found ourselves obliged, in dealing with the general
theory of the reflex process, to assume the existence of a certain
disposition or tendency due to the original interconnexion of
fibres in the central nervous system. The theory explained the
increasing limitation of the reflex response in the life of the
individual by the supposition that the connexion of sensory and
motor nerves is the most direct possible, i.e., that it represents
the path most usually followed by an excitation-process.

Impulsive and Volitional Action 385

But when we said just now that the connection of the mimetic
movements with emotion was ' original for the individual/ there
was implied the possibility of pushing our investigation beyond
the limits of the individual life. The question now becomes ^
problem in evolution.

You know that Darwin based his hypothesis of the origin of
species by ' natural selection ' upon two principles, — the prin-
ciple of variability and the principle of inheritance of individual
characteristics. It is surely evident that these cannot be meant
as really explanatory principles, but only as general rubrics,
under each of which are included a whole number of problems
to be solved. For our present purpose, however, it is enough
to remark that, whatever their ultimate causes may be, they are
undoubtedly as valid for mind as they are for body. Suppose
that both conditions, variation and inheritance, have been at
work for an indefinite time, and that the physical peculiarities
of the organic world have differentiated it more and more ;
there will also be constant differences to be found in mental
disposition or tendency. The perfection and differentiation of
species as regards body and as regards mind constitute, that is,
two parallel processes of development. When certain nerves,
muscles, and central organs habitually function in response
to psychophysical impulses, their physical development must
necessarily follow suit ; while, on the other hand, furtherance
of physical development means increase of mental function.

If we apply this hypothesis in our special case, it seems quite
adequate to explain the appearance of connate impulsive actions
observed in the new-born child. There is no reason why in
the course of many generations certain nervous fibres and ner-
vous cells should not advance in development and others recede,
new ones be produced and old ones disappear. Even as between
different individuals of the same species the number of these
elements may differ very considerably. And the differences of
family, race, and species arise through the summation of these
individual variations by inheritance ; while upon the develop-
ment of the separate parts of the nervous system and its terminal
organs depends further the capacity of a simultaneous excita-

C C

386 Lectures on Human and Animal Psychology

tion of different parts of the body, i.e., the inclination towards
combined movements of some particular kind.

We may therefore regard the conditions of the development
of impulsive movements as at once physical and psychical. Let
us suppose that there exists an organism with the very simplest
nervous system, consisting, say, of a few cells and connecting
fibres. The impulsive movements called forth in such a creature
by sense-stimuli will be altogether irregular. But very soon
particular sensory fibres, which, owing to their position or for
some other reason, are more frequently stimulated from without
than their neighbours, will begin to develop more strongly.
The immediate result will be a corresponding development of
the motor fibres most directly connected with them. In this
way a connexion will be formed, which may be perpetuated ;
i.e., which will be present in the individual's descendants from
the very first. Regarded from the psychical side, this process
•appears as a gradual restriction of the effect of emotion to those
actions which call forth feelings similar to the emotion in
-affective tone, and which thus enter into intimate association
•with it. The association cannot, of course, be inherited as such.
But since the corresponding physical connection within the
nervous system is transmitted from one generation to another,
the impulsive movement in the individual is just as reflexly
certain a response to the central excitations underlying emotion,
as it is to external sense-impressions whose effect for feeling is
analogous. In this way the affective associations which have
been gradually acquired in the course of a long generic develop-
ment may be present from the first, and require but little further
development by individual practice.

At this point it becomes evident that no hard and fast line
can be drawn between impulsive and expressive movement.
Every impulsive action is a consequence, and therefore an
expression of emotion. The animal which, impelled by its
desire for food, throws itself upon its prey, is thereby giving
expression to a state of mind dominated by emotion just as
certainly as the man who expresses his grief by tears. The
only difference is, that in expressive movement in the narrower
sense the external action has no special purpose ; it has no
direct effect upon the satisfaction of the pleasurable or painful

Impulsive and Volitional Action 387

feeling connected with the emotion. In this sense the expressive
movements are rudiments of impulsive movements. But very
frequently the more active emotions, such as anger or the
pleasure in a coveted object, pass directly over into impulses
and impulsive actions proper. Anger, e.g., becomes transformed
into the instinct of revenge, and this finds its expression in
movements which seek to satisfy the revengeful feeling by an
injury done to the object of anger. Impulse, that is, bears the
same relation to emotion in the internal experience as impul-
sive action bears to expressive movement. And just as in the
development of mental life impulsive action is the earlier, and
pure expressive movement, — a mere relic of it, — necessarily
the later, so the universal animal impulses, — the impulses of
nutrition, of sex, of revenge, of protection, etc., — are indubitably
the earliest forms of emotion. Or if we wish to express the
same thought in somewhat different language : the emotions
are impulses which have become complex, but which in pro-
portion to their complexity have lost their characteristic of
activity.

We are able, then, to distinguish impulsive action from pure
expressive movement by the fact that the former has a definite
purpose, which is consciously attained or at least attempted,
while the latter, though it shows some faint indication of a
purpose, does not imply the least consciousness of intention
to attain it. In saying this, we are at the same time charac-
terising impulsive action as voluntary action. This, and this
alone, is the criterion of voluntary action : that the thought of
the end to be realised accompanies or precedes it. Impulsive
action, therefore, is simple voluntary action in the sense ex-
plained above (Lecture XV., p. 228).

Again, when a feeling is transformed into an emotion, it takes
part in an ideational movement which is itself accompanied by
feelings. Generally some particular idea stands out in this
movement as the efficient cause of the process ; and arouses the
appropriate impulsive action either simultaneously with its own
appearance or directly afterwards. If at this stage a number of
partial emotions combine to form one compound affective state,
there may plainly be present together in consciousness a
number of conflicting motives. And so there is developed, in

388 Lectures on Human and Animal Psychology

natural order from the simple, the compound voluntary action,
or act of choice. At any one of these stages voluntary action
may be mechanised to reflex action : the steps have been
described above in the course of our description of the separate
conscious processes (Lecture XV.). The pure expressive move-
ments also fall under this law of mechanisation ; their ac-
companiment of the emotions has ceased to be a matter of
consciousness and volition.

§111

Movements which originally followed upon simple or com-
pound voluntary acts, but which have become wholly or partly
mechanised in the course of the individual life or of generic
evolution, we term instinctive actions. ' Instinct ' is derived
from instingiiere, to incite or impel ; and in meaning, as by
definition, it comes very near to impulse. The only difference
between the two consists in this, — that ' impulse ' is generally
used to denote the simpler purposive movements; 'instinct'
to denote the more complex impulsive actions, which pre-
suppose a long course of individual or generic practice.
Instinctive action, therefore, stands midway between reflex
movement and pure voluntary action. Thus the mimetic
movement which follows the application of an acid stimulus to
the tongue will be counted as a reflex ; hardly regarded as
instinctive. But the involuntary movement of defence that a
man makes when a stone is thrown at him we shall be inclined
to term an instinctive action. It is evident enough that it must
often be difficult to draw any very definite line between move-
ments which have become entirely mechanical and those that
still contain the impulsive element. Under certain circumstances
the mimetic reaction to acid may be impulsive. Indeed, this
will happen fairly often, i.e., whenever there is at once asso-
ciated with the acid taste the impulse to keep the tongue away
from the stimulus. On the other hand, the movement of
defence may appear as a simple reflex, occurring before the
impression of danger has come to consciousness at all. This
uncertainty of definition, combined with the current psycho-
logical restriction of the concept of will to choice, explains how

Theories of Instinct 389

it is that the chapter on instinct is one of the most debated
fields in the science, notwithstanding that the now universal
recognition of the genetic view of animal life in general has
removed the principal obstacle to the comprehension of the
more complex animal instincts.

§ IV

Still even to-day the theories of instinct form a regular
museum of conflicting opinions. Some regard it as a purely
mechanical result of the physical organisation, a compound
reflex movement, only different from the simple in that the
motor responses to particular stimuli are more complicated and
extend over a longer period of time. Others look upon the
instinctive action of animals as a manifestation of connate ideas.
A third view considers it as voluntary action, involving con-
sciousness of end or purpose, but characterised by diminution in
the clearness of ideas. The two last hypotheses have in modern
times been gradually superseded by a fourth and fifth, which
have grown up under the influence of the theory of evolution.
These, together with the first (the pure reflex hypotheses), may
be regarded as the standard theories at the present day. The
first of them makes instinctive actions ' mechanised rudiments
of manifestations of intelligence.' It emphasises the opinion,
especially with reference to animal instincts, that this mechani-
sation has been going on for countless generations. The second,
of which Darwin is the representative, explains instinct as
inherited habit, determined principally by the influences of the
environment and the struggle for existence, but also to some
slight extent by intelligence. Like all habit, instinct has been
subject to change ; but natural selection has brought it about
that these changes have always been purposive, advantageous
to the species.

We may reject at once as wholly untenable the hypothesfs
which derives animal instinct from an intelligence which, though
not identical with that of man, is still, so to speak, of equal
rank with it. At the same time we must admit that the ad-
herents of an intellectual theory in a more general sense are
right in ascribing a large number of the manifestations of

390 Lectures on Human and Animal Psychology

mental life in animals not, indeed, to intelligence, as the
intellectualists sensu stricto do, but to individual experiences,
the mechanism of which can only be explained (as we saw
above) in terms of association. The precautions which the
spider takes in fastening the threads of her web, and in selecting
a suitable spot for it, point quite decisively to associative
. mental activity. The same is true of the many alterations
made by honey-bees in the ordinary structure of their comb
when they are disturbed by pieces of glass or other objects
introduced into the hive. Indeed, it is probably impossible to
adduce a single instance of instinct in which the actions of the
animal do not afford evidence of some amount of individual
experience. At the same time, there is another and parallel
class of actions to be taken account of, which, although wholly
purposive, cannot either be interpreted as the outcome of
teleological reflection, or be explained from impressions and
associations experienced during the individual life. When the
bird builds her nest, or the spider spins her web, or the bees
construct their comb, these are distinctly purposive actions ;
indeed, they are more purposive than the other actions of the
same animals which are explicable in terms of individual
experience. If it were really teleological reflexion that led the
bird to build her nest, the spider to spin her web, and the bees
to make their comb, we should be compelled to attribute to
these animals a degree of intelligence which the experience of
a single life could hardly be expected to develope even in man.
Another argument that makes against this explanation is
the regularity with which the same actions are repeated by the
different members of a single species in cases where no con-
nexion can be demonstrated between the various individuals
such as might possibly account for the uniformity. Of course,
there is an intimate connexion existing between the inhabitants
of the same hive or ant's nest, and between parents and young
in the species in which the family holds together for some little
time. But in numberless instances the animal begins its life in
total independence of its fellows. When the caterpillar hatches
out of the egg, its parents are long since dead ; nevertheless, it
spins the cocoon that they did. And, lastly, to interpret
instinctive action as intelligence would in very many cases be

Theories of Instinct 391

to predicate of it a prevision of the future. It is hard to suppose
that this prevision is conscious when there are neither analogous
experiences given in the previous life of the individual, nor any
way by which they could be communicated to it. The night-
flying phalcena covers the eggs which it has laid with a layer of
fur made from its own hair, to protect them against the cold,
before the winter has come. The caterpillar changes into a
chrysalis without any experience of the metamorphosis which
it is to undergo.

We cannot better demonstrate the impossibility of a deriva-
tion of instinctive action from conscious reflection than by
quoting an illustration from an earlier author, in which all the
contradictions which the theory involves are brought together
into short compass. The caterpillar of the emperor moth spins
at the upper extremity of its cocoon a double arch of stiff bristles,
held together above only by a few fine threads. The cocoon,
i.e., opens at the very least pressure from within, but is able to
resist quite strong pressure from without. Autenrieth writes of
this in his Ansichten uber Natur- und Seelenleben : ' If the cater-
pillar acted from reflection and with understanding, it must, on
human analogy, have pursued the following train of thought :
that it had reached its chrysalis stage, and would therefore be
at the mercy of any unlucky accident, without possibility of
escape, unless it took certain precautionary measures in advance ;
that it would have to issue from its cocoon as imago without
having organs or strength for breaking through the cover it had
spun as caterpillar, and without possessing any secretion, like
other insects, which would if emitted eat through the threads of
silk ; and that consequently, unless it took care to provide as
caterpillar a convenient exit from its cocoon, it must certainly
come to a premature end in imprisonment. On the other hand,
it must have clearly recognised during its work upon the cocoon
that, in order to have free egress as imago, it would only be
necessary to construct an arch which could resist attacks from
without while opening easily from within ; and that these con-
ditions would be fulfilled if the arch were made of stiff threads,
inclined together in the median line, and with their ends left free.
At the same time it must have realised that the plan could be
carried out if the silk employed for the construction of the other

392 ^Lectures on Human and Animal Psychology

parts of the cocoon were employed with special care and skill at
the upper end. Yet it could have learnt nothing of all this from
its parents : they were dead long before it had issued from the
egg ; it had had no practice or experience, for the spinning of
the cocoon happens only once in a lifetime ; it could not imitate
a neighbour, for the species is not a social one. And during
the whole of its existence as caterpillar its understanding could
have been but very little developed : it crawled about on the
branch where it first saw the light, devouring leaves, an occupa-
tion which required no consideration, since the food was there
waiting for it ; it clung fast with its feet, perhaps, to avoid falling
to the ground, and crept under a leaf to escape the rain ; it got
rid of its old uncomfortable skin some few times by involuntary
contractions of its entire body, but without making any cocoon :
—and that was the whole of its life, the sum of its opportunities
for the exercise of intelligence.'

Instinctive action, then, cannot be explained either in terms
of conscious reflection or from individual associations : the
hypothesis requires an amount of prevision on the part of the
animal which is psychologically impossible. But the opposite
theory, recently defended by Herbert Spencer, that instinctive
action is simply compound reflex action, determined by the laws
of the physical organisation, is equally untenable. That the
caterpillar secretes silk, the spider the material for her web, and
the bee wax, is just as much a matter of physical necessity as is
the emission of any other secretion. But that these substances
when secreted are worked up in such definite and artistic forms
is altogether inexplicable from the facts of physical organisation.
That accounts for the material which the animal has at its dis-
posal, but not for the form, which is the real result of its work.

Worse still, if that is possible, is the view which stands mid-
way between the intelligence and reflex theories, and which
regards connate ideas as the motives of instinctive action. The
bee is supposed to have in its mind from the first a pattern of
its hexagonal cell, the spider a pattern of the meshes of her web,
the caterpillar a picture of its cocoon, and the bird one of the
nest it is to build ; and each of these animals must necessarily
translate its idea into reality. The older philosophical idealism
found in such a hypothesis a welcome support for the doctrine

Theories of Instinct 393

of innate ideas. But it contradicts everything that our analysis
of the human consciousness has taught us. It is impossible to
prove the existence in our own minds of ideas which do not
spring from the experience of the individual life. The congeni-
tally deaf has no knowledge of tone, the congenitally blind none
of colour. And the probability that complex ideas can be
innate is infinitely less. Besides, the observation of instinct
does not by any means give unqualified support to the hypo-
thesis. If there is so definite an image of the hexagonal cell in
the bee's mind, how is it that all the cells of the hive are not
made of the same size ? You see, there must be present in its
consciousness not the idea of a single cell, but that of the whole
number of cells belonging to the colony, if its action is to
become intelligible in every respect. The bird builds its nest of
certain determinate materials, from which it never varies except
in cases of necessity. Does the innate idea of the nest include
the ideas of every twig and straw used in its construction ? It
is evident that this theory becomes entangled in difficulties no
less grave than those which proved fatal to the hypothesis of
intelligent action. It requires the assumption not of a single
innate idea, but of a whole connected series, in a word of an
innate activity of thought with a large store of experience
behind it.

Only two hypotheses remain, therefore, as really arguable.
One of them makes instinctive action a mechanised intelligent
action, which has been in whole or part reduced to the level of
the reflex ; the other makes instinct a matter of inherited
habit, gradually acquired and modified under the influence of
the external environment in the course of numberless genera-

o

tions. There is obviously no necessary antagonism between
these two views. Instincts may be actions originally conscious
but now become mechanical, and they may be inherited habits.
This compromise would have a great deal to recommend it, if
we might slightly alter the first theory, and make instinct,
according to it, partly a matter of mechanised volition and
partly of action which is still determined by psychical motives.
If we are ourselves to appeal to the facts for a decision in favour
of one of the two views or for a verdict for or against a combi-
nation of both, we shall do well to keep in mind the rules laid

394 Lectures on Human and Animal Psychology

down above in connection with our consideration of the mani-
festations of animal 'intelligence' (Lecture XXIII.). Never have
they been so sadly sinned against as in this particular chapter
of psychology on the nature of animal instinct. The first ran,
you remember, that we must always set out from known facts
of the human consciousness ; the second, that simple principles
of explanation are always to be preferred to complex.

We must, therefore, go on in the following lecture to discuss
briefly the instinctive actions in man. When we have done
that, we may pause to look back once more upon the very
difficult phenomena presented by animal instinct.

LECTURE XXVII

I. INSTINCTIVE ACTION IN MAN. § II. ACQUIRED INSTINCTS. § III.
CONNATE INSTINCTS. § IV. PRACTICE, IMITATION, AND INHERIT-
ANCE. § V. RELATION OF ANIMAL TO HUMAN INSTINCT.

BY an instinctive action we understand,~as remarked above,
something purposive, but involuntary, half impulsive and
half reflex. It cannot be doubted that in this sense many
human activities come under the category of instinctive action.
We laugh and weep, we make the most complex mimetic
movements, without, or even against, our wish or our know-
ledge. Most of our movements are determined by emotion,
and volition manifests itself quite as often in the moderation or
inhibition of movements as in their independent initiation. Not
seldom the will simply makes definite the direction of a move-
ment ; its execution is left to instinct. When we walk, it is
generally volition that prescribes the road ; but step follows step
instinctively. Many actions at first require practice and the
exercise of voluntary effort, but when once they have become
familiar, may be performed under almost exclusively instinctive
control. The child learning to write will laboriously copy every
stroke of the pen ; the ready writer needs only the intention to
write some particular word, and it stands before him on the
paper. The novice at the piano must strain his attention upon
every note, in order to find the appropriate key ; the practised
player translates the printed page mechanically into the proper
movements. Any movement that has become altogether
habitual is made instinctively. An impulse of will is, of course,
necessary at the outset ; but its effect extends to a whole series
of actions, and each particular one takes place without effort
and without knowledge : the series once started is continued to

395

396 Lectures on Human and Animal Psychology

its end with the same unconscious certainty and purposiveness
as the reflex. The voluntary movements of early childhood are
uncertain and awkward ; practice has not had time to transform
them into instinctive acts. And the same is true of the adult
whenever he wishes to perform some as yet unaccustomed
action, of however simple a character. Precision and grace of
movement, then, depend upon certainty of instinct, not upon
firmness of will.

This transformation of voluntary into instinctive activity is
greatly furthered by the influence of the environment. From
the first days of life we are surrounded by our fellow-men, and
imitate their actions. And these mimetic movements are in-
stinctive in character. As soon as the child's consciousness is
aroused from its first sleepy passivity, it begins to perceive the
expressions of others' emotions, and to respond to them by
similar emotions with corresponding impulses. The continued
imitation by which a child comes to learn the language that is
spoken round it is impulsive, not voluntary. Even the peculiar
word-formations of child-language are not, as is often wrongly
held, invented by the child, but borrowed by it from its environ-
ment,— from the words of nurse and mother, who in their inter-
course with it adapt themselves to its level of mental develop-
ment and capacity of articulation. And with them, again, this
formation of special baby-words and imitative sounds is to a
very slight degree a matter of purposed invention ; for the most
part the adaptation and imitation are themselves instinctive.
Voluntary act and instinctive movement, suggested by environ-
ment and example, cross and recross in human conduct from
the beginning to the end of life. And if the sum of action
resulting from personal choice and intellectual reflection were
laid in one scale, and that proceeding from instinct and imita-
tion in the other, there can be little doubt that the beam would
incline on the side of instinct. Suppose a bird were to become
interested in zoological investigation ; he might well regard man-
kind as the richest of all creatures in instincts. Man shares
with the birds the instinct to live in wedlock ; like the fox, he
educates his children ; he has the beaver's impulse to build
houses, and the bee's custom of founding states and sending
forth colonies ; while he has in common with the ant a pleasure

Acquired Instincts 397

in war, in slave-making, and in the domesticating of useful
animals.

There is, it is true, one immense difference. In man all these
instincts, at least in the form which they have assumed in the
course of history, are the fruits of a continuous intellectual
development, not a trace of which is demonstrable among the
animals. And a great gulf is set up also by the fact that within
the limits of these general norms of life individual volition has
ample space for the determination of its particular conformity
to them. Still, if human conduct as a whole is divided into the
two great departments of voluntary and involuntary action,
there can be no doubt that for the vast majority of us the
principal incentive to those very acts which constitute the
universal criterion of the genus homo is not reflection and free-
will, but instinctive imitation of our neighbours. Reflection and
volition begin as a rule only when the general norms of life
have to be applied in the particular case. How the individual
builds his house, or where he lives, may be a matter of pro-
tracted consideration for him. But that mankind at large build
houses and seek shelter seems to him to be as natural and right
as it probably does to the bee to construct its hexagonal cells.
And even the question of the particular disposal of his own life,
which is so tremendously important for the civilised man,
generally troubles the savage but little. He builds his hut or
pitches his tent as his fellows do, and as his forbears did before
him. So that human life is permeated through and through
with instinctive action, determined in part, however, by intelli-
gence and volition. As for that, all forms of psychically con-
ditioned action are mixed processes. It hardly ever happens
that a fact of consciousness admits of complete subsumption to
any of the categories that psychological abstraction enables us
to set up. Like mental life in general, it contains a mixture of
v irious elements.

§ "

Instincts which, so far as we can tell, have been developed in
this way during the life of the individual, and in the absence of
definite individual influences might have remained wholly un-
developed, may be called acquired instincts. You can see from

3 98 Lectures on Human and Animal Psychology

what has been already said that all and each of them, — from the
instinctive finger-movements of the practised pianist down to
the instinct to build a shelter and wear clothes for protection
against the weather, — spring from two conditions, one physio-
logical and the other psychological. The former consists in the
property of our nervous organisation gradually to mechanise
complex voluntary movements ; the second, in the operation of
the mimetic impulse, which is probably natural to all animals
that live in any kind of society, but is especially powerful in
man. This impulse is itself an instinct ; mimetic movements
are, as a rule, impulsive, and not volitional. But it is at the
same time the fountain-head of many other instincts, and
especially of those whose development is furthered by a social
mode of life. It is a necessary corollary from these remarks
that the first of the two conditions will be effective, even if the
second be absent, in the case of the acquired instincts sensu
stricto, — instincts developed during the individual life as a result
of individual practice, such as the instinctive movements of the
skilled pianist. These are purely matters of physiological
practice ; so that it is not difficult to understand that the move-
ments may occasionally become quite reflexive. The hypothesis
which is most nearly adequate to this special case, then, will be
the fourth of those which we reviewed above as professing to
account for instinct in general : — that of the passage of intelligent
into reflex action. I say ' most nearly ' : for the expression ' in-
telligent action ' is not admissible in the present instance, any
more than in the other contexts in which we have discussed it.
In most cases there are no acts of intelligence involved at all,
but only associations ; and in any case intelligent action must
have been reduced to association before it could become mecha-
nised. The piano-player has first of all to form a stable associa-
tion between the printed note and the movement of touch. But
this association gradually lapses from consciousness, and the
interconnection of movements becomes purely mechanical.

The operation of the second condition, the psychological
impulse toward imitation, is to be seen, — often enough in com-
bination with the physiological factor, — in the case of the .social
instincts. The fact which lies at the root of the imitative im-
pulse »s this, — that as a rule any action resulting from psychical

Connate Instincts 399

motives excites in all individuals of the same species an emotion
similar to that experienced by the agent himself. And similarity
of emotion means similarity in its external expression. The
simplest manifestations of the imitative impulse, then, will be
found in the different forms of violent emotional expression.
The passionate gestures of a speaker are reflected in the in-
voluntary movements of his audience. As we look at a terrified
or sorrowful face, our own features assume a cast in keeping with
the feelings it expresses. In all these cases the imitative move-
ments are purely instinctive. On the other hand, if the strange-
ness of the presentation is such as to evoke an act of will on our
part, the instinctive reaction passes over into some less simple
form of action. This is seen in all the human social instincts,
where the sphere of instinct borders on that of custom. The
phenomena here are of a kind so mixed and complex, that their
instinctive element is usually entirely overlooked.

To be distinguished from these acquired human instincts are
others, which are connate. They are, perhaps, more modified in
man than in the other animals by civilisation and education ;
but they are still indispensable for the origin of the most
important vital functions. There are in particular two funda-
mental instincts of organised nature, — the impulses of sex and of
nutrition, — which appear unchanged in man, as connate instincts.
The investigation of the conditions of connate instinct in general
is exceedingly difficult. But that, of course, is so much the
more reason for starting out from the facts of the human con-
sciousness, which furnish the only directly accessible observa-
tional material.

Do connate instincts spring from connate ideas, or do they
depend upon intellectual processes ? You will see at once that
such hypotheses as those could never have been set up had not
mankind been left out of account in their formulation. Or is
the impulse to imitation in some way or another a factor in their
constitution, as in that of the acquired social instincts ? To this
question also we may return a negative answer, without more
words. Are we, then, to look on these manifestations of original

400 Lectures on Human and Animal Psychology

instinct as something analogous to the mechanised voluntary
actions that now resemble reflexes ? Certainly, if you observe
the first sucking movements of a new-born mammal, those that
appear before it has satisfied its hunger by actual sucking of
milk, you will not find much to object to in the term ' reflex.'
But none the less it is impossible to suppose that these reflexes
have originated in a similar way to the mechanised movements
(say those of the pianist) that have come about by practice. No !
so long as we confine ourselves to the life of the individual, there
can be no question that they are original, and not acquired. It
looks, thereforej as though we had found an exceptional case to
support the reflex theory, which has proved untenable every-
where else.

But we must not decide in its favour too hastily ; we must
go to observation for refutation or confirmation. The reflex
theory assumes that the sucking movements of the new-born
mammal are not only involuntary, but unconscious. Like
reflex movement in general, they are purely physiological in
nature : they show an entire absence of psychical motives.
Now, though such an assumption might look reasonable enough
on the study-table, it is hardly a theory that any one would
hold who had ever really seen the movements of a hungry
infant Every feature and every gesture betoken the presence
of unpleasant feelings. Plain enough to read in its crying
and movements is the inarticulate complaint : ' I am hungry.'
Give it anything that can be sucked, a finger or a corner
of its pilloxr. All movement ceases ; sucking, and only sucking,
is the business of the moment. It is not long, of course, before
the restlessness comes back again, only to be finally overcome
by the satisfaction of hunger.

It is wholly impossible that all this is a matter of purely
physiological reflexes. If emotional expressions have any
significance at all, the infant's movements can only be inter-
preted as psychically conditioned actions, i.e., manifestations of
impulse. No doubt we must suppose that in these first impul-
sive movements there is not present a shadow of the idea of
th- end towards which the impulse is directed. But that is
not at all necessary for the origin of emotional and impulsive
expression. Sensations, with the feelings attaching to them,

Connate Instincts 401

are altogether adequate to the result. And they are given
in the sensation of hunger, which is physiologically conditioned,
and the unpleasant feeling connected with it.

At the same time, there is one part of the effect that these
causes do not suffice to explain, — the very phenomenon which
gives to these impulsive movements their character of pur-
posiveness, and renders it possible for them to attain their
end : — namely, the sucking movement of the lips, which is
in no sense a characteristic of unpleasant emotions in general.
None the less we may regard this as a special emotional
expression, inseparably associated in the human infant with
the intensively toned sensation of hunger. And if the move-
ment is one of expression, its purposiveness becomes intel-
ligible. For while expressive movements are the means of
expression of individual emotions, their general nature and in
particular their characteristic of purposiveness result from a
process of development extending beyond the individual : their
physiological conditions are inherited or, what in this connec-
tion is the same thing, were acquired in the course of earlier
generations, reaching back into an unlimited past. And this
shows us the grain of truth that is contained in the reflex
theory. The sucking movements of the new-born child are
reflexes, in the sense in which expressive movements in general
are reflexes. Their purposiveness, like that of the reflexes, is
due to an organisation acquired in the course of generic, not
individual, evolution. But they differ from the reflexes proper
in this, that they are accompanied by emotions in the mind,
and that their performance is regulated by these emotions.
It is just the combination of these two characteristics that
constitutes the peculiarity of the connate impulse. It stands
midway between the reflex and the acquired impulsive action :
related to the former in that its ultimate basis is physiological,
and to the latter in that it springs directly from psychological
conditions, which may at any time interfere to modify its
original character.

D D

402 Lectures on Human and Animal Psychology

§ IV

If we survey all those phenomena of human conduct which
are referable to instinct, we see that the simplest conditions
of instinctive action in general are to be found in the cases
where it is the result of individual practice. Here the action
simply indicates a disposition of the physical organisation,
which has been induced by movements often repeated in the
past. The performance of a definite complex act and its con-
nexion with an adequate sense-stimulus have become more
and more matters of course ; till at last they are rendered
completely mechanical. In the second place come the ac-
quired social instincts, whose conditions are complicated by
the development of the social emotions and the corresponding
mimetic actions. Lastly, the connate instincts oblige us to
assume that the disposition of the physical organisation plus
the mechanisation of complex movements correlated with it,
if induced through a number of generations, leaves behind it
permanent physical effects, common to all individuals alike ;
so that certain impulsive movements, subserving the ele-
mentary necessities of life, take on the reflex form. They
may then constitute a starting-point for fresh developments,
through which the impulse can arrive at a special degree of
perfection in special individuals.

The effect of ' practice ' and ' habit ' can only be due to
after-effects of excitation, of the kind assumed by us for the
explanation of instinctive movements. And since the expres-
sions of instinct are par excellence ' customary ' or ' habitual '
actions, their subsumption to the general law of practice needs
no justification. That law runs as follows : the more fre-
quently a voluntary action is repeated, the easier is it to perform,
and the greater is the tendency of its constituents (if it is a
complex act) to take on the reflex form, i.e., to arrange them-
selves in a connected series of movements, which runs on
mechanically when once initiated by an adequate stimulus.

The formulation of this law shows us at once that its basis
must be physiological. The goal attained by the process of
practice is simply the mechanisation of movements which were
originally dependent upon psychical antecedents. That must
mean that mechanical, i.e., physiological, alterations of the

Practice, Imitation, and Inheritance 403

nervous system are at the bottom of the whole matter. We
are still so much in the dark as regards the real nature of
nervous processes, that we need not be surprised to find the
exact physical and chemical character of these alterations
quite unknown. If we know nothing more about them, we
are at least certain that they exist ; the witness of the actual
results of practice cannot be called in question. There is
hardly any movement of the human body, however difficult,
which we cannot, by continued practice and repetition, reduce
to a mechanical certainty so complete, that it will be performed,
even without any intention on our part, as the necessary
reaction to certain sense-stimuli. Very remarkable instances
of this mechanisation of complex actions by practice occur
now and again in the conduct of ' absent-minded ' persons.
It is quite a common experience to begin a customary action
at a time which is altogether unsuited for it, — the stimulus
having been given by some familiar impression. We may
intend to pass by our own house or the place of our daily
business, but suddenly discover that we have mechanically
followed our usual route, and entered the building without
in the least meaning to do so. Some years ago I was occupied
with certain physiological experiments on the frog, each of
which involved the performance of a fairly complicated opera-
tion. It happened one day that I had taken up a frog for the
purpose of making a quite different experiment. I suddenly
found, to my great astonishment, that, instead of making the
intended experiment, I had performed the customary operation.
Now we certainly cannot regard acts of this kind as pure
reflexes. The impressions are not only physiological stimuli,
but psychological motives as well. But the reaction to them
is impulsive : the familiar visual impression calls up the sensa-
tions, feelings, and movements associated with it. The move-
ment could not, however, become instinctive in that way
unless the succession of movements had been thoroughly prac-
tised physiologically. The greater the extent of this practice,
the more effective is the inhibition of the conscious realisation of
what we are doing, which puts a stop to the unintended action.

There are experiences of the most different kinds, then,
which put the physiological effects of practice beyond the

404 Lectures on Human and Animal Psychology

shadow of a doubt. But there is yet another proof of their
reality in the functional properties of the nervous elements.
If you excite a motor nerve by a stimulus so weak that it
only just occasions a contraction of the muscle attached to
it, and continue to apply this same stimulus at intervals just
sufficient to avoid exhaustion, you will find (especially if the
nerve is in good condition) that the contraction gradually
increases in amount. This increase of excitability by stimula-
tion can be best seen in the reflex movements that follow the
stimulation of a sensory nerve connected with the cord, —
supposing always that the experiment is made under condi-
tions which preclude the adverse influence of fatigue. The
molecular changes in the nervous elements on which the
increase of excitability depends are, as was said above, still
unknown. But we can get some idea of them by taking a
few common illustrations of the facilitation of a movement
by its repetition. As a carriage-wheel, for instance, turns
round the axle, the rough surfaces are gradually worn smooth ;
the frictional resistance is diminished. A watch, as you all
know, goes better the more regularly it is wound up : and
so on. Similarly, we may suppose, repetition facilitates the
functioning of the nervous elements by removing all manner
of obstructions and inhibitions. Now a complex muscular
movement consists of a definitely arranged sum of simple
movements, every one of which depends upon some element-
ary excitation-process. Each preceding excitation in such
a series serves as the adequate stimulus for the succeeding
one. This means that the effect of practice consists not only
in the facilitation of every particular component of the com-
plex process, but also in that of the definite combination
of elementary movements which go to make it up.

You can easily see that this law of practice possesses a
significance for the physical basis of our mental life which
extends far beyond the sphere of instinctive action. Not only
the combinations of certain movements, but the associations
of sensations and ideas in general, are rendered stable by
practice. Contiguity- and similarity-associations alike bear wit-
ness to its influence. The former are directly correlated with
the habitualness of certain excitatory processes in a sense-

Practice, Imitation, and Inheritance 405

centre, the effect of which is to facilitate the genesis of sensa-
tion when the same impression is repeated ; the latter depend
upon our habituation to a particular connection of simulta-
neous or successive excitations. Regarded from this point of
view, that is, instinct appears as an extension of association
to the motor sphere.

These laws of practice suffice for the explanation of the
acquired instincts. The occurrence of connate instincts renders
a subsidiary hypothesis necessary. We must suppose that the
physical changes which the nervous elements undergo can be
transmitted from father to son. Later generations will then
be affected in two ways : they will from the first acquire
familiarity with certain complex movements more easily, owing
to connate dispositions of the nervous system ; and they will
react to particular stimuli by reflex movements of mechanical
certainty, owing to particular nervous dispositions of a more
definite and clearly marked kind. The assumption of the
inheritance of acquired dispositions or tendencies is inevitable,
if there is to be any continuity of evolution at all. We may
be in doubt as to the extent of this inheritance : we cannot
question the fact itself. It is in particular the inherited reflexes
of the human infant, so important for the development of its
instinct of nutrition, that belong to those constituents of ori-
ginal disposition which reach far back to the beginnings of
generic development. But more individual gifts, — the trans-
missibility of certain talents is unquestionable, — also appear to
lend probability to the view that the propagation of definite
dispositions takes place, at least within certain limits. Disposi-
tions of this kind, however, are not the products of any very
long development ; and are probably to be looked on rather
as dispositions facilitating the practice of new functions than as
ready-made systems of reflex arcs. It is of great importance,
by the way, in this matter of the transmissibility of more
special gifts, that the disposition of associations and the direc-
tion of instincts be in complete agreement. A connate talent,
especially if its field of exercise is internal rather than external,
depends at least as much upon the disposition to form certain
associative connexions as upon the facility of certain complex
forms of movement. But in every case the point to remember

406 Lectures on Human and Animal Psychology

is that it is the disposition, not the actual functional capability,
which is connate. Every instinctive action, however original it
may be, — the taking of food by the infant, e.g., — must to a
certain extent be acquired afresh by the individual. Far more
practice, then, will be required for the realisation of the connate
talent, which has so short a period of development behind it.
Readiness of movement and many-sidedness of ideational con-
nexion are the promise of the connate disposition ; the fulfil-
ment of the promise comes later in life. Ideas cannot be
inherited any more than complex volitional actions. Talent
and instinct alike are latent until external stimulation calls

them into actual life.

<•

§ V

We have now reviewed the conditions of origin of the human
instincts. How does the matter stand with the analogous
phenomena presented by the animal kingdom ? Are they de-
ducible from the same conditions, — perhaps with the difference
that the various factors are concerned in different amounts ?
Or must we look for other and peculiar explanatory reasons ?

Different in expression as animal and human instincts are,
their fundamental similarity can hardly be doubted. The first
question must be answered in the affirmative, the second in the
negative, though the negation cannot be absolute : for the
conditions of human life are such that in it certain influences
tend to disappear, and may accordingly be left out of account,
which acquire a very considerable importance in the life of
animals. To see the necessity of this admission, we have only
to cast a glance at instincts which enable an animal, — e.g., a
caterpillar, — to provide not only for itself, but also for its larval
condition and even for a still later condition, that of the imago,
without the aid of the example of other animals or of any
previous experiences of its own. Can the principles which our
explanation has adopted explain this, — that a caterpillar living
in a pomegranate cuts a way out of the fruit just before its
transformation, and then makes this particular part of its home
fast with silk thread to the nearest branch, that it may not fall
to the ground before the transformation is complete ? Many
similar instances are quoted by Darwin in a posthumous essay

Relation of Animal to Hiiman Instinct 407

on instinct, published as an appendix to Romanes's work
Mental Evolution in Animals, Here belongs, too, the case
of the caterpillar of the emperor moth, which we employed
as an argument against the intellectualistic hypothesis (p. 391).
These are all connate instincts ; so that the closest analogy to
them in our own experience would be furnished by the sucking
movements of the hungry infant. But these are sufficiently
simple to be referred to a ready-prepared reflex mechanism.
Can the same be said of the complicated animal actions which
conform so wonderfully in the different species to the special
conditions of life ? And, granted that it can, how far will the
previous life-history of the species enable us to explain the
origin of the particular reflex mechanism ?

We do not know the details of this life-history. And there-
fore we must give up any hope of a real genetic explanation
of instinct. All that we can do is, first, to test the general
question of the possibility of the origin of reflexes, which do not
simply involve a definite and unchangeable co-ordination of
movement and stimulus, but a co-ordination which may vary
with variation of its special conditions ; and, secondly, to
inquire whether the term ' reflex ' is really applicable to the
facts as stated. Now it is true that brainless animals exhibit
reflexes of the kind that varies with its special conditions.
A frog the whole of whose brain has been removed, with the
exception of the optic lobes, not only tries to escape when its
skin is stimulated, but avoids obstacles placed in its way. But
in other respects the movement has all the characteristics of a
reflex. Apply this to the present case. There can be no doubt
that here, too, variations occur in accordance with special con-
ditions ; if only for the reason that (as our previous discussion
shows) the movements, like those of the hungry infant, are not
purely reflexive, but expressive of emotions, — the expression
being mediated by preformed purposive connections within the
nervous centres. So that, strange as the instinctive action of
an animal like the caterpillar may at first sight appear, it yet
differs only in degree from the action of the human infant,
which we have found comparatively easy of explanation. *

1 For a description of the various animal instincts, cf. G. H. Schneider,
Der tliierische Wille (1880). Unlike so many works upon the same subject,

408 Lectures on Human and Animal Psychology

There still remains one point which requires further elucida-
tion. Hitherto, relying upon the facts of human experience
we have been bridging the difference between connate and
acquired instincts in this way : we have supposed that father
can transmit to son the physiological dispositions that he has
acquired by practice during his own life, and that in the course
of generations these inherited dispositions are strengthened and
made definite by summation. But is it possible to conceive of
any specific life-history into which there could be crowded such a
multitude of tendencies as should finally give rise to a succession
of instinctive actions so complicated as those of the caterpillar,
of the emperor moth, or even of the bird of passage, which
flies south in winter without precept or example ? Surely the
analogy of the practised pianist fails us here. But is it really
applicable even to the connate instincts of man ? Do not they
imply besides the action of will, which is required to introduce
what afterwards becomes habit, a compelling force residing in
the external conditions of life ? We do not know from what
beginnings the functions of nutrition have been developed in
man, except in so far as the facts of structural evolution admit
of functional inference. But his general mental attributes en-
able us to assume quite definitely that the earliest development
and consolidation of habit took place under the conjoint and
unfailing influence both of external circumstances and of volun-
tary actions proceeding from feelings.

And this leads us to the principle which Darwin enunciated
as of prime importance for the development of instinct and for
the course of evolution in general, — the principle of adaptation
to environment. There can be no doubt that this adaptation
and 'voluntary action constitute the two universal determinants
of the development of animal impulses. The first supplements
the second ; volition must have an object towards which it is
directed. The converse, of course, need not necessarily be the
case. In the vegetable kingdom specific alterations are gradually
effected by the sole operation of the environment, influencing
the functions of growth or favouring certain peculiarities which
are thus more readily and certainly perpetuated. And this

this volume may be recommended as giving an impartial and accurate
account of observed facts.

Relation of Animal to Human Instinct 409

passive adaptation will naturally be found among animals as
well, since they share with plants all the physiological functions
which are capable of modification by it. But Darwin's explana-
tion of the development of instinct as being mainly the result
of passive adaptation seems to contradict the facts. Instinctive
action is impulsive, that is voluntary action : and however far
back we may go, we shall not find anything to derive it from
except similar, if simpler, acts of will. The development of any
sort of animal instinct, that is to say, is altogether impossible
unless there exists from the first that interaction of external
stimulus with affective and voluntary response which constitutes
the real nature of instinct at all stages of organic evolution.
We may possibly succeed in deriving a complicated form of
instinct from a more simple one ; but we can never explain in-
stinct in terms of something which is as yet neither instinct nor
impulse.

External conditions of life and voluntary reactions upon them,
then, are the two factors operative in the evolution of instinct.
But they operate in different degrees. The general development
of mentality is always tending to modify instinct in some way
or another. And so it comes about that of the two associated
principles the first, — adaptation to environment, — predominates
at the lower stages of life ; the second, — voluntary activity, — at
the higher. This is the great difference between the instincts of
man and those of the animals. Human instincts are habits,
acquired or inherited from previous generations ; animal instincts
are purposive adaptations of voluntary action to the conditions
of life. And a second difference follows from the first : that the
vast majority of human instincts are acquired : while animals, —
apart, of course, from the results of training, which do not con-
cern us here, — are restricted to connate instincts, with a very
limited range of variation. This makes it to a certain extent
intelligible that the older psychology, failing to see the close
connection of habit and practice with instinct, usually ascribed
instinctive action to the animals alone and denied it to man.
The corollary from that connexion really is, that animal instinct
is more predominantly reflexive, more exclusively constituted of
purposive movements given with the connate physical organisa-
tion. If the complexity of a number of instinctive actions in

410 Lectures on Human and Animal Psychology

animals seems to contradict that view, you must remember that
throughout the animal kingdom they remain relatively uniform.
We might almost say that the whole organisation of the central
nervous system seems in many cases to be determined by certain
associations that have been established by instinct

LECTURE XXVIII

§ I. SOCIAL INSTINCTS ; TEMPORARY ASSOCIATIONS AND FRIENDSHIPS
OF ANIMALS. § II. ANIMAL MARRIAGE. § III. ANIMAL SOCIETIES
AND STATES.

§ I

NEW and peculiar conditions for the development of in-
stincts are to be found in the common life of animals.
This is, of course, a product of social instincts ; but it
reacts in the most various ways upon the original impulses
which occasioned it.

At the very lowest stages of animal life we see every crea-
ture seeking its like. Many of the medusae and molluscs,
many insects and fish, unite temporarily in swarms or schools.
In all such cases it is not the individuals, but the species, which
know one another. At the same time, the origin of the social
impulse can only be looked for in a feeling of inclination, how-
ever primitive, which attracts animals of the same species
towards each other by the intermediation of certain sense-
impressions, — perhaps of smell or sight. At a higher stage of
development this feeling of inclination shows itself as an indi-
vidual attraction of animal to animal. But this is not found until
we come to the higher birds and mammals. Dogs, as you of
course know, manifest very pronounced likes and dislikes. If
two poodles, e.g., are kept in the same house, there may spring
up between them a kind of friendship ; the survivor mourns the
loss of his comrade. Horses from the same stable become
similarly attached to one another. Most remarkable are the
friendships which arise between animals of different species as
a result of living together. Even a dog and a cat may become
friends. The inclination in all these cases is purely individual.
The dog will pick out his comrades from a score of other dogs ;
and however gracious his behaviour to a particular cat, will
chase all her companions with true canine hostility.

412 Lectures on Human and Animal Psychology

§ H

When the feeling of individual inclination combines with the
sexual impulse, we have the phenomena of animal marriage.
We can only speak of marriage when the union of male and
female for the fulfilment of the sexual functions is a permanent
one, demonstrably based upon individual inclination. There is
no trace of it among the invertebrates or the lowest vertebrates.
Although the ' insect-states ' are really extended families, there
is no proof that their individual members know one another as
such, or are held together by any permanent mutual inclination ;
indeed, the facts enumerated in Lecture XXIII. make such a
hypothesis exceedingly improbable.

On the other hand, marriage is a very common phenomenon
among birds and mammals. That our domestic animals furnish
so many exceptions to the rule is probably the result of domesti-
cation. By close association with man, the animal loses touch
with its kind. Most animals are monogamous, although poly-
gamy is a well-known institution among birds. Polyandry does
not appear to have been observed in animals ; it is confined to
certain savage tribes.

We have many reliable observations to show that with many
birds the marriage contract is a matter of free choice. Males
and females that are kept together in a cage by no means always
pair. There are preferences and aversions shown, for reasons
often inexplicable to ourselves. Male song-birds contend for
the females in song. The birds of paradise are said to spread
their gorgeous plumes till the female chooses the wooer that
pleases her best. Animals of a fiercer disposition do not get
through their wooing so peaceably ; the males generally have to
fight pretty vigorously for the object of their choice. Lions and
tigers wage bloody war for the possession of a spouse ; and stags
will wound one another to the death in their struggle for a doe.
The males of polygamous species are especially ferocious in
this quarrel for wives : you know that two cocks in the same
yard are impossible. In this matter of choosing a mate, peace-
ably or otherwise, recourse is always had to the special weapons
and peculiar ornamentation that so frequently characterise the
male animal : think of the antlers of the deer, the spur of the

Animal Marriage 413

gamecock, the tusk of the boar, the lion s mane, the varied
plumage of many birds. All the birds that breed with us, —
pies, storks, swallows, sparrows, doves, and what not, — are mono-
gamous. The nest is nearly always the family residence ; male
and female build it together, and share in the tending of eggs
and young. Only the swallows have separate nests for male
and female. Besides the common fowl, the ostrich and the
cassowary are polygamous.

The marriage-relation among animals takes on a different
form in monogamy and polygamy. The cock looks after his
hens, seeks food for them ; they follow his call. But the hen
does nothing for the cock except obey him. On the other hand,
she watches, feeds, and protects the chicken, while the cock does
not trouble himself about them. In monogamy it is generally
otherwise. A pair of pigeons share all there is to do between
them. Male and female take turns in sitting, and both alike see
to the feeding of their young. It is obvious that these differ-
ences depend upon differences in the feelings of individual
attraction ; and we shall therefore be right in explaining by
their aid the difference between the monogamous and poly-
gamous form of the marriage-relation.

The stability of animal marriage seems in general to be pro-
portional to affection for the young. And this again becomes
stronger the more careful and lasting attention the brood
requires. A secondary reason for the continuance of the union
after the young have ceased to require care is the need of
mutual aid and protection. This holds especially of animals
which construct nests or lairs, or which live in holes. So far,
therefore, animal marriage is intimately connected with the
conditions of specific physical organisation. But it would be
unwarrantable to ascribe all its phenomena to this source.
Individual inclination certainly determines choice in animals as
well as in man ; accidental contiguity is a second and different
cause. If there is an intimate connection between the fulfilment
of a mental impulse and the satisfaction of a physical necessity,
that is no more than we find everywhere else in our investigations
of life and mind.

414 Lectures on Human and Animal Psychology

§ HI

In marriage individuals are held together by the feeling that
they belong to one another. If this feeling is extended so far
as to embrace a large number of animals, we have an animal
society. Most birds and mammals tend to unite in flocks or
herds. Domestication may overcome this tendency ; but it is
seldom absent in the wild or feral state. Even dogs that have
run wild not infrequently get together into a pack. Our oxen
and sheep have retained the impulse to social life even under
domestication. Many animals herd only for a particular purpose,
especially for plunder or food ; but even then the herd is very
often composed of a definite group of individuals. Migrant birds
flock only when about to migrate ; the passage is made by
thousands together. At its conclusion the individuals separate,
to reunite in the following autumn. In the meantime the only
connexion that the members of the same flock have with one
another is that of locality ; they generally settle down near one
another. A flock of daws likes to settle, if possible, all together
in the same ruin ; storks of the same flight nest in neighbouring
villages. There seems to be evidence in all these cases that the
primitive feeling of inclination which brings the members of a
species together at the very lowest stages of animal life is rein-
forced by individual inclinations, though there may be but few
in every flock or herd that are held together by them.

We are taken a step further by animals which construct
interconnected lairs or holes, destined to contain not one family
only, but the progeny of a whole colony. This inclination is a
direct outgrowth from the impulse of the individual to build.
The otter tends to settle down in the neighbourhood of other
otters. The same is true of the hamster and the beaver. Some-
times the partitions between nest and nest are broken down,
and the whole system thrown open ; as is the case with the
hiding-places of rats and mice.

These forms of social union are common enough. A special
place among them must be assigned to the so-called insect- states ;
'' so-called,' for they are not really ' states.' The expression
applied to these animal communities has done more to mislead
than to explain. It has led to the assumption that all their

Animal Societies and States 415

phenomena are to be interpreted in terms of those of human
governments and institutions ; which in its turn tempted ob-
servers to parallel the division of labour in these societies,
conditioned by the facts of physical organisation, with class
distinctions in human society, and so to explain their observa-
tions by reading into them their own thoughts and feelings.
We have already had illustrations of this method of procedure
in our review of ant-life (Lecture XXII I., p. 343).

Insect-states are really extended families. The dwelling-
places of the colonies are nests of a more or less complicated
structure, according to the size and composition of the society.
In most cases those orders of animals which contain the species
that live in states include others which have not carried their
social life farther than the stage of simple nest-building. In
some species of wasps, — e.g., the digger-wasps and solitary wasps,
— the males and females live separately, though the female digs a
hole in the mortar or wood of a wall, in which she lays her egg,
putting in small caterpillars along with it, to serve as food for
the newly hatched larvae. The nest of the common wasp is more
•extensive. In the spring the female builds in a tree, on a roof,
or in the ground a few hexagonal cells of vegetable material,
lays an egg in each of them, and feeds the newly hatched larvae
until they crawl out. After this the young assist in the work
of building, and a nest is gradually constructed, the female
depositing an egg in every new cell. The females that develope
at this period are themselves incapable of laying eggs ; their
whole energy is consumed in the business of nest-building, and
their sexual organs remain immature. These sexually unde-
veloped females are accordingly called workers. Not till towards
the end of the summer are eggs laid which produce males and
perfect females. These males fertilise the females in the autumn.
When cold weather sets in they and the workers die ; but the
females survive the winter, and at the return of spring begin to
make nests and lay eggs. The female solitary wasp generally
begins her work in some narrow hole in a wall, into which she had
crept for the winter ; and the colony issues forth later, when the
space has grown too small for it, to build a larger nest. What
is true for the wasp holds also for the humble-bee (bombus), a
relative of the ordinary honey-bee. The female is fertilised in the

4t6 Lectures on Human and Animal Psychology

autumn, survives the winter, and begins an underground nest in
the spring, in the building of which she is assisted by the females
or workers which are first hatched. Towards the end of the
summer sexually mature insects make their appearance ; and
with the coming of winter the whole colony perishes, with the
exception of the females which seek shelter underground.

There are two features in particular of these communities of
wasps and humble-bees which for a long time defied any attempt
at interpretation : the presence of sexless workers among perfect
males and females, and the constancy with which the appear-
ance of the latter two forms was restricted to the end of the
summer. The first problem was solved so soon as it became
known that the workers were not really sexless, as had been
supposed, but simply immature females. This arrest of develop-
ment could easily be explained from the expenditure of force
necessary for building the nest ; and experiment showed that a
more abundant supply of food did really suffice to change the
workers into ordinary females. The second problem was
answered by the discovery, first made in the case of the honey-
bee, that the laying of male or female eggs depends entirely on
the nature of their fructification by the female herself. After
fertilisation by the male, the female retains the injected seed in
a small pocket opening into the canal by which the eggs escape.
This arrangement is of immense importance, because in these
insects all eggs, even those which are not fertilised by the male,
are capable of development. The fertilised eggs produce female,
the unfertilised male insects. It is now plain why the humble-
bee and the wasp at the beginning of summer lay only eggs
which develop into females : the female fructifies her eggs as
long as she retains any of the seed which she received from the
male the autumn before. When this store is exhausted, the eggs
can only produce males. But even of the fructified eggs it is
only those last laid that can become perfect females, because it
is only after the completion of the nest and the production of a
sufficient number of workers that the larvae are well enough fed
to attain to their complete development. So that what looked
at first sight like a preconceived design in these simplest insect-
states proves to be the necessary result of physical organisation
and of the relatively simple instincts which accompany it.

Animal Societies and States 417

Taking the wasp as our guide, we shall not, perhaps, find it
so very difficult to explain the organisation of the bee-state.
The female bee, the ' queen ' as she is called, also lays fertilised
and unfertilised eggs. But she lays both kinds from the first, and
distributes them among the cells of the hive, which the workers
have built from wax of their own production. The cells are of
two kinds, — wide and narrow. The wide are for the unfertilised
eggs> which develope into males or drones ; the narrow for the
fertilised, which develope into workers. Besides this, the queen
lays a few fertilised eggs in specially wide cells. The larvae from
these are fed more abundantly than the rest ; they become per-
fect females or queens. Sometimes the workers will take a larva
from an ordinary cell into a royal cell which is not quite finished ;
then by means of good nourishment it becomes a queen. Irv
the spring, as soon as the brood of queens is beginning to-
approach maturity, the hive becomes restless ; and on the first
fine day a part of its inhabitants swarms out in quest of a new
abode. This first swarm is quickly followed by others ; so that
a single hive may found several colonies in the course of the
summer. The old queen always goes with the first swarm,
leaving the hive before the brood of new queens are out of their
cells. The first of these latter to appear remains queen of the
hive ; the others fly off with a portion of the workers to found
other colonies. If two queens of the new brood make their
appearance simultaneously, they fight till one or the other is
overcome and killed, unless she avoids her danger by swarm-
ing out in time. The hive, therefore, never contains more than
one sexually mature female, though the number of drones is
very various, ranging from none at all to nearly a thousand.
The drones are not confined to the limits of their hive. In the
spring they fly out on every warm day and meet the young
queens. But in the autumn, as soon as provisions become scarcer,
they are expelled by the workers, and perish on the first cold
night.

What distinguishes the bee's hive from the societies of wasps,
hornets, and humble-bees, therefore, is a more hard and fast
division of labour. In containing only one female, the hive re-
sembles the nests of these other insects. But it is essentially
different from them in its mode of origin. The wasp's nest is

E E

418 Lectures on Human and Animal Psychology

begun by a female, so that her solitariness is a matter of course.
But the bee's hive is a society from its foundation, a society
which grows, but without undergoing any radical change. The
solitariness of its queen is partly the result of force. But it is
this very interconnection of bee-states, the fact that each is a
colony from some pre-existing one, that enables us to under-
stand the mode of origin of the bee-societies and their difference
from the associations of related insects. The natural history of
the building of every wasp's nest is just a repetition of the same
processes. But the bee-state stands in connection with its parent
state, that again with its own, and so on. It has, in other words,
a historical relation to the past and the future. If we suppose
that there occur in such a society expressions of the universal im-
pulse towards imitation, it is a necessary corollary that a colony
•will not have to begin its life from the beginning, but carries to
its new home the customs acquired by previous generations,
whether these are transmitted in inherited organic dispositions
or are perpetuated by being directly handed down from the
older insects to the younger. But it would be altogether gratu-
itous to assume that the organisation of the hive has always
been what we find it to-day. We know from experience that
the habits of animals may change. One can wean the domestic
insects from swarming and founding colonies by enlarging
their hive as circumstances require. Populous bee-states will
now and then give up the work of collecting honey, and take to
plundering the smaller hives in their neighbourhood. And if
we see changes like these in the habits of animals going on
under our eyes, there is nothing to prevent our concluding
that the peculiarities of the bee-society have arisen gradually
and slowly, and that its customs have been fixed and settled
both by inherited physical dispositions and by imitation. This
conclusion is all the more probable in that the mode of
origin of the beehive of to-day contains indications that its
primitive mode of origin was something different. The first social
union of the insects, you see, cannot possibly have branched off
from any pre-existing society. How could it have been brought
about ?

The question is answered by the condition in which we still
find certain of the insects that are most closely related to the

Animal Societies and States 419

honey-bee. Every female wasp founds her own family ; every
female bee must originally have founded her own family in the
same way. Worker and queen at once, she prepared by her-
self the first cells for her brood. Now an alteration in these
conditions may have been brought about by the greater length
of life of the bee-communities. When more than one female had
appeared in a single hive, jealousy made any peaceable common
life impossible ; death and exile were the only alternatives for
the weaker faction, and the latter would have been already
suggested whenever the crowded condition of the nest pre-
vented any further increase of population. So far everything
is intelligible. But how is it that the queen voluntarily de-
posits drone-eggs in the wide cells, and worker-eggs in the narrow
ones, and that the workers kill the royal larvae if the weather
is unfavourable to swarming ? These customs, too, we have
every reason to suppose, are matters of gradual development,
products of the natural evolution of instinct. The size of the
cells in which the larvae develop, e.g., would have to be settled
by reference to their wants. At first all the cells might have
been made of one size. It would soon be found that the more
poorly nourished larvae, which were destined to become workers,
required less space than those which turned into queens or
drones. When once the right size had been hit upon, it might
be adhered to in the future, since the bee-state is in touch with
past traditions which lay down rules of conduct for its
members. The younger generation had only to follow the
example set them by their elders. For this reason the bee-
state never needs to return to the primitive stage, and model its
organisation from the very beginning. There is no exaggeration
in saying that it is based, like our own civilised states, upon the
work of all preceding generations.

Ant-communities differ from those of bees chiefly in the number
of females which they support. For the greater part of their
lives the males and females are winged ; and they are larger
than the wingless neuters which make up the great bulk of the
population. These neuters, like the worker-bees, are immature
females. With the ants, too, the division of labour seems at
times to extend even to the workers : especially with the ter-
mites, or white ants of Africa and Southern Asia. These anta

420 Lectures on Human and Animal Psychology

build hills which often attain the height of several feet. Their
workers are of two classes, — the workers proper, to which the
peaceful avocations of the colony are entrusted ; and the soldiers,
whose duty it i? to attack strange nests or defend their own
from attack. This difference in instinct is probably correlated
with difference in the physical strength of the individuals. And
everything that we know of the intellectual capacities of these
insects would lead us to suppose that the division of labour is
not consciously agreed upon. A very similar instinct is dis-
played by the Amazon ant, which carries off the larvae from the
nests of weaker species, and makes workers or ' slaves ' of them.
This instinct is rooted in the general aversion that the different
species of ants manifest towards one another, and has been
gradually developed from the mob-fights in which the feeling
of mutual dislike often culminates. Another specific instinct of
ants is the custom of keeping plant-lice as ' domestic animals,'
for the purpose of feeding themselves and their larvae from
the liquid secreted in the abdomen of these animals. There is
nothing strange in such an expression of the nutritive im-
pulse : the plant-louse, being one source of food among others,
would naturally be carried with the rest into the ant-hill.

The phenomena presented by these animal states can only be
seen in their proper light, if we keep in mind at the same time
the mental capacities of the individuals which compose them. I
have already pointed out to you that the exaggerated ideas
of the early bee and ant naturalists as to insect intelligence
must be considerably modified in view of the results of obser-
vations made under careful experimental conditions. The
members of a bee- or ant-community do not know one another
individually. And the feeling of inclination which holds them
together is of a collective, indefinite nature, standing on a far
lower developmental plane than the analogous feelings of birds
and mammals, which lead to marriage or to the formation of
less extended associations. The power of communication is
also extremely limited, confined in all probability to certain
manifestations of the imitative impulse. Numerous proofs of
the comparatively low development of the mental life of the
individual in these insect-communities have been collected by
Sir John Lubbock, to whose work upon ants, bees, and wasps

Animal Societies and States 421

I must refer you, in the absence of any observations of my own.1
His investigations show clearly enough the immense advantage
of experiment in this field over simple observation. Lubbock ap-
proached every single question with pre-conceived ideas, derived
from observation of the general results of instinct and naturally
tending towards an overestimation of the intellectual capacities
of the insects. But experimental tests always gave the same
result, — that the impulses of the common instinct left hardly any
place at all for the exercise of individual intelligence or the ex-
pression of individual feelings of inclination. And even
l^ubbock's conclusions require one further limitation ; this con-
cept of intelligence still plays far too great a part in his
pages. The very modest performances which he ascribes to
intelligence are entirely explicable in terms of comparatively
simple associations. And that implies that the feelings and
impulses operative in the instinctive actions of the insects in
question are of an extremely primitive kind. So that when
we talk of their having feelings of inclination and aversion, or of
their impulse towards imitation, we must be careful not to
regard these feelings and impulses as identical with the analogous
processes of our own consciousness, still less with these pro-
cesses plus the products of our reflection upon them. We have
before us no more than the first obscure movings of feelings and
emotions, which we do not find in their clearly conscious form
till we reach the higher animals or even man, but which for
that very reason act with all the greater certainty and uniformity
at this low level of development. We are fatally inclined to
make the same mistake with regard to the elementary psychical
factors, feelings and impulses, which lead to the formation of
animal societies that we make in foisting our own point of
view upon their complex results, — these communities themselves.
We talk of the organisation of insects into a state, of .queens and
workers, of soldiers and slaves, even of the rearing of domestic
animals. And so we tend to read into their loves and hates,
acts of succour and of imitation, conscious processes completely
analogous to those which the terms call up in our own minds. We

1 Ants, Bees, ami Wasps : a Record of Observations on the Habits of
the Social Hymenoptera, by Sir John Lubbock, Bart., M.P. (Int. Sci.
Series).

422 Lectures on Human and Animal Psychology

must remember that we are really in face of very primitive
forms of mentality, which may be every bit as different from its
more highly developed stages as is a single cell from a complex
organism.

But if we are always obliged to measure the animal mind
by the standard of our own consciousness, applying this as best
we can where the conditions are so different, the other side
of the matter is not less important. We must look into these
facts of animal psychology for light upon the phenomena of the
human mind. Another fatal tendency on the part of the
psychologist is to measure every human action by the highest
standard applicable to it. We look at it from the standpoint of
intellectual reflection, and then make this reflection, — our own
affair entirely, — the condition of its origin. Man lives in wed-
lock ; he combines with his fellows to form a community ; he
founds states. All this as he does it presupposes an immense
sum of intellectual work, accumulated through countless genera-
tions and implying the development of the higher feelings.
In every particular case of human action this accumulated store
is drawn upon. But it is surely wrong, in the light of the
instances which the animal kingdom furnishes of the manifes-
tation of social impulses, that a part played in the constitution
of human society by original, natural impulse should be so
entirely overlooked as it not infrequently is. Why, even in man
it is only the special development which the phenomena have
undergone, not their existence or their origin, which is the result
of civilisation. The witness of animal psychology tells with
all possible directness for the naturalness of the first beginnings
of human social life. The investigation of the interaction of the
two factors, nature and civilisation, in their gradual develop-
ment forms the subject-matter of other disciplines upon which
we cannot enter, — social psychology and social science.

LECTURE XXIX

§ I. VOLUNTARY ACTION. § II. THE CAUSALITY OF WILL. § III.
RELATION OF THE INDIVIDUAL TO THE GENERAL WILL. § IV.
CHARACTER AS THE ULTIMATE CAUSE OF WILL.

§1

WHEN we were considering will in its significance as an
elementary psychical phenomenon, we found that the
facts comprehended under the term constituted the
links in a chain of development. The lower stages of this de-
velopment, simple voluntary acts, were classed together as,
manifestations of impulse ; the higher stages, acts of choice, as
those of volition proper. In reviewing the expressions of in-
stinct we have become familiar with a whole number of pheno-
mena whose invariable mental condition is some impulsive act,
while at the same time the peculiarities of the physical organi-
sation exercise a determining influence upon their development.
It now remains to consider briefly the second and higher form of
voluntary activity, volition proper, in its relation to the entirety
of conscious processes.

We took our best examples of instinctive action from the
animal kingdom. In the present investigation of volition, on
the other hand, we are exclusively restricted to the human con-
sciousness, although it is certain enough that instances of
volitional action are not infrequent in the animal world, and
especially among its more highly organised members. But the
problem of volition, or, as it is generally called in consequence
of the popular restriction of the concept of will to the sphere of
choice, the problem of will, is practically confined to man, for
this reason, — that the one question which is of decisive import-
ance for our understanding of the nature of voluntary action and
its relation to the other facts of our inner experience, a ques-

424 Lectures on Hitman and Animal Psychology

tion which has long divided psychologists and philosophers
alike into two hostile camps, is one that must be answered by
an appeal to our own minds. It is the question of the causality
of will.

§11

An impulsive action is one, as we have seen, which is uni vo-
cally conditioned ; there is only one motive present in conscious-
ness. Volitional action arises from the choice between different
motives, clearly or obscurely conscious. In impulse, therefore,
the feeling of our own activity is less developed than in volition ;
whilst, since this latter involves a decision as between various
conflicting motives, the feeling of our own activity rises in it to
that of freedom.

But if freedom is a result of the possession of will, of the
choosing or selective will, how does it come about that the re-
lation of the two is so often transposed ? Instead of saying, ' I
am free, for I can will,' we are apt to say, ' I can will, for I am
free.' Is not this a confusion of cause and effect? It is plain
enough that our consciousness of freedom can only have its
source in the power of willing. The prisoner is not free, be-
cause his will is without effect. He would gladly be out of
prison : but that is wishing, not willing. A firm belief in our
power to do is an indispensable condition of willing, which is
just the decision to act. How, then, are we to explain the fact
that the consciousness of freedom, whose root is in the will, thus
denies its origin, and makes itself out to be the cause of that
from which it has really resulted ?

We know that we are free when we act of our own power,
unimpeded by any external obstacle. Action by our own power
we term volitional action, and regard as the consequence of our
freedom. But what do we suppose to be the cause of this free-
dom ? There appears to be at this point a sudden break in the
chain of cause and effect. We say the very concept of freedom
excludes any idea of causality. For if it were dependent upon
some cause or other, it would cease to be what it is, — freedom.
Freedom and necessity mutually exclude each other.

Notice now the steps by which we have arrived at this con-
clusion. We should not be justified in saying the very concept

The Causality of Will 425

of will excludes any idea of causality. For the fact that we dp
not know all the causes of a volition cannot be regarded as
necessarily implied in the concept. What is done, then, is this.
Freedom, the concept of which excludes causality, is interpolated
as a middle term, on the one side of which volition is subject to
causality, while on the other it is independent of it. For it is
now subjected to a special causality, the causality of freedom,
while made independent of general causality, the causality of
natural processes.

It is this view of the matter which has given rise to the con-
flict between ordinary determinism, which maintains the uni-
versal validity of the law of causation, and indeterminism, which
postulates freedom. * The will cannot be free,' says the deter-
minist, ' for a free will would not accord with the actual causal
connexion of world-processes. Natural law would be replaced
by miracle. No! every action, however free it seems, must have
its cause. It is a necessary occurrence, and the agent cannot
help himself.' ' The will is free,' replies the indeterminist, ' for
we have an immediate consciousness of its freedom. Natural
necessity and personal freedom are opposites. But the latter is
vouched for by the inner voice of conscience, requiring from
the agent responsibility for his every action.'

The opponents of the freedom of the will, that is, assert that
its assumption is nonsense ; its advocates maintain that it is
necessary. Which party in the dispute is right ?

We must insist, in the first place, that all the ethical arguments
which have been brought to bear upon the question of the free-
dom of the will are out of place. They may move us ; they may
incline us to the hypothesis of the freedom of human volition :
they cannot prove anything. Even if a denial of the freedom of
the will imperilled the validity of conscience and shook the
foundations of our whole ethical system, still, if clear proof
could be adduced that the will is not free, science would have to
take its course. But happily that is not the case. Whichever
theory holds the field, practice may stay quietly at home. You
may remember what Kant said : ' Every being who can act
only under the idea of freedom is in his action really free ; that
is, he is governed by all the laws which freedom would neces-
sarily bring with it, just as really as though his will were proved

426 Lectures on Human and Animal Psychology

to be free to the satisfaction of theoretical philosophy.' The
undeniable fact that we have a consciousness of freedom makes
fatalism impossible, unless, indeed, this consciousness itself be
regarded as included in the universal causal nexus. For this
consciousness of freedom tells us that we have the power to act
without being consciously impelled by any constraining force,
external or internal ; it does not tell us that we act without a
cause. The defenders and the opponents of the freedom of the
will have not seldom been at one in their confusion of constrain-
ing force and cause. Really, the two are wholly disparate con-
cepts. We cannot say the earth is constrained to move, but we
can say man is constrained to die. Only a being who knows
that he is free can be constrained. The fatalist makes the mis-
take of destroying freedom and putting constraint in its place,
constraint being in actual fact a condition which arose out of
freedom, and cannot be conceived of without it.

So that if we take the concept of freedom in its proper sense,
we shall say, ' The will is free,' for everything that stands in the
way of a purposed voluntary action is felt by consciousness as
constraint, while will seems to it the very opposite of this con-
straint. Freedom and constraint are reciprocal concepts ; they
are both necessarily connected with consciousness ; outside of
consciousness they are both imaginary concepts, which only a
mythologising imagination could relate to things. If we say,
1 The earth is subject to constraint because it moves round the
sun,' we might just as well go on to assert that the sun is free,
because it moves the planets.

Herbart remarks somewhere: ' If we regard ourselves as not
free, we are really not free ; but if we ascribe freedom to our-
selves, it by no means follows that we are so in reality.' We
may say with equal justice : ' If we know the cause of a pheno-
menon, it necessarily follows that this really has a cause ; but if
we do not know the cause of a phenomenon, it by no means
follows that it has no cause.' But it is this last and erroneous
inference which the adherents of absolute indeterminism draw
when they conclude, from the premise that we cannot discover
in consciousness all the causes which determine the will, that the
will itself is the first cause of our actions.

Tt was attempted to support this negative proof from con-

The Causality of Will 427

sciousness by a further positive argument. In nature, we are
told, every occurrence presupposes a previous condition of things
of which it is the inevitable consequence. This previous con-
dition must itself have a predecessor, and so forth. But for the
beginning of this infinite series we must postulate a primary,
spontaneous impulse, if the origin of the world is to become in-
telligible at all. Now if it is once shown that one point stands
outside of the universal causal nexus, there is no difficulty in
conceiving of any number of causally connected series arising in
the progress of the world's development, and each possessing
its own particular beginning. If I now undertake the perform-
ance of some voluntary action, this fact, with all its consequences,
means the beginning of a new series, each term of which is
determined by natural causes except the first one, which is be-
yond their reach.

There are two weak points in this argumentation. In the
first place, the assumption of a first beginning of things seems to
be impossible for consciousness, whether pictorially or concep-
tually represented ; and secondly, even if a first beginning of
the world had to be assumed, the hypothesis that similar be-
ginnings could take place in the midst of the course of the
world's development would be an analogical inference, destitute
of all positive foundation.

The fundamental error in these and other arguments for or
against the freedom of the will goes deeper. It consists in con-
sidering the entire question simply under the concept of natural
causation. The very first requisite is a treatment of it as a
question of psychological experience. If we regard it from this
point of view, we see at once that the psychical causes, whether
of a voluntary act or of any other manifestation of consciousness,
are never wholly discoverable, for two reasons : first, because they
lie outside consciousness, and belong to an inaccessible series of
past experiences ; and secondly, because they form part of a more
general conscious nexus, of which the individual mind constitutes
only one link. The general direction of the individual will is,
you see, determined by the collective will of the community in
which its possessor lives. And it is particularly in this connec-
tion that we find reason for the belief that the causality of our
mental life cannot be subsumed without more ado under the

428 Lectures on Human and Animal Psychology

familiar laws of natural causation, such as that of the equivalence
of cause and effect.

§ HI.

An attempt to construct the history of a nation or of mankind
at large in terms of the laws of natural causation would not
only be vain in practice : it would be wrong in principle. If the
individual can say that, in place of acting as he did in some par-
ticular case, he might have acted otherwise, we must also be able
to say of every event in history that it might have happened
differently. In both cases the necessity of natural causation is
wanting. For historical events and for the voluntary actions of
an individual we can -only adduce determining motives ; we
cannot prove constraining reasons. In this regard the concepts
of historical occurrence and of voluntary action are exactly
equivalent. The only difference is, that one refers to a com-
munity, the other to an individual.

The general will of a community consists simply in the ex-
pressions of the wills of a large number of individuals. The
individual and his voluntary action are enclosed within concen-
tric circles of more and more general volition. First comes the
general will of the little community in which he most immedi-
ately belongs ; then he, with this will, is subject to the will of a
larger community ; with this, again, to a still more comprehensive
will ; and so on. The relations in which the individual is thus
placed are the principal determinants of his voluntary actions.
But the general will of a community is usually in its turn
determined by the wills of the more energetic individuals, which
are acquiesced in by the individual wills of the majority.

It is a rule written upon the face of history that the frequency
of expressions of volition is inversely proportional to the mag-
nitude of their effects. National action by which the course of
history is suddenly changed is a matter of rare occurrence.
Events which we can refer to the action of the general will of
considerable communities constitute, as it were, the milestones
of history. In the intervals between them the general will is for
the most part inactive ; though there are changes occurring
within the community, oscillations in this direction or in that,
they are not of vital import: they are like the variations of an

Relation of the Individual to the General Will 429

individual will in obedience to the impulses and emotions to
which a man's manner of life exposes him. The determination
of the general will by those of a few prominent individuals has
given place to its direction by a crowd of hardly noticeable in-
fluences, affecting each and all alike, directly or indirectly, by
way of external condition or internal modification.

The principal determinant of the individual will is, as we have
seen, the will of the community. In stirring times the course of
events carries the individual with it, while in those periods of
history when the general will is inactive the community remains
in what we may call a state of equilibrium. But the social con-
dition resulting from previous history, from external natural
causes, and from the intervention of particularly strong indivi-
dual wills in the ordinary progress of things, must, of course,
itself contain motives of determining influence upon the voluntary
action of the individual ; so that it is only to be expected that in
the long intervals elapsing between historical events of the first
magnitude the practically constant condition of society will bring
with it a certain uniformity in the voluntary actions of the
individuals composing it

This general influence is confirmed by statistical facts. We
find that the annual number of crimes, suicides, and marriages
may remain constant for decades together, in civilised countries
where the condition of society resulting from their past history
is also approximately constant. Ouetelet showed that the num-
ber of marriages every year is more regular even than the
number of deaths, to which, of course, — except in cases of suicide,
— the will has nothing to say. The same statistician proved also
that so long as the course of justice, the prosecution and punish-
ment of crime, remain unaltered in any nation, the crimes
committed show a marvellous constancy in number, character,
and distribution with regard to age and sex. And the same
regularity obtains for suicide. It extends even to the manner
of death chosen. Every year approximately the same number
of men hang, shoot, poison, and drown themselves. From all
this constancy we cannot but conclude that the historically de-
termined social condition of a people is a dominant influence in
the voluntary actions of the individual citizen.

And our conclusion finds still further confirmation in observa-

430 Lectures on Human and Animal Psychology

tions of a different nature, which afford us the means of isolating
certain of the factors which combine to constitute the state of a
society. If we compare the slight deviations from absolute
regularity which the statistical tables show with the relations
which help to determine that state, we are able in some measure
to trace them to their causes. Thus it is demonstrable that
famine increases the number of crimes against property and
decreases the number of marriages. Violent epidemics, like
cholera, bring with them a temporary decrease in the number of
marriages, followed shortly after their disappearance by a still
more marked increase. This latter phenomenon is to be
ascribed to the increased mortality occasioned by the epidemic.
Society seems to be hastening all unconsciously to fill up the gaps
that death has made in its ranks. However irregular the actions
of the individual, those of the community present the completest
uniformity. But this regularity appears as the product of a blind
necessity. Actions of every kind follow a definite numerical law,
which no volition of the individual can avail to change.

But if in this summation of individual actions there is no trace
of anything that could be ascribed to the influence of an indivi-
dual will, are we not bound to conclude that this influence is
illusory? Is not the exception to natural law only an apparent
one, which disappears when our observations extend over a
sufficiently wide field ? Yes ; this conclusion has been drawn.
The statistical figures prove, it has been said, that voluntary
actions are dependent in measurable degree upon a series of
external factors. Will within us, that is. corresponds to acci-
dent in the natural world without. Neither is a phenomenon
without laws ; but both are phenomena whose laws cannot be
deduced from the particular instance. In this way, it has been
thought, the problem of the freedom of the will is solved by
appeal to experience ; and the solution is — determinism.

But there is nothing in the facts of statistics to warrant such
a conclusion, in the remotest degree. They simply show that
the influence exerted by the condition of society constitutes
one of the causes which determine the will. Whether it is the
only cause, or whether there is not a whole number of co-ordinate
causes to be found elsewhere, — on those questions they have nui
a word to say.

Relation of the Individual to the General Will 43 1

In extending our observations from the individual to a large
community, we eliminate all the causes which condition the in-
dividual alone or only some small section of the community.
It is the same procedure as is employed in physics. To elimi-
nate chance influences which might vitiate the result of an
observation, a large number of observations are taken. The
more observations there are, the more probable it becomes that
the separate sources of disturbance, which work in both directions
as plus and minus, will compensate one another ; so that the
average of the whole number will give us a result in accordance
with the real fact under observation. But when we argue that,
because statistics enable us to cancel out the influences that
are restricted to the individual, therefore these influences do not
exist, that is as bad as it would be to say in physics that the
accidental errors, eliminated in the total number of observations
were not present in the particular case. The physicist can
afford to neglect them, simply because they possess no signifi-
cance for him ; the psychologist cannot. The question before
him is whether there exist, in addition to the influence exerted
by the social state of a community, further determinants of
volition of a more individual character. He must not neglect
the deviations from the norm shown in the particular case ; for
their presence constitutes the proof that such secondary deter-
minants really exist.

Statistics itself teaches us that the effect of individual condi-
tions determining voluntary action can really be traced in
different degrees in the different circles of a community. The
number of crimes, suicides, and marriages varies with age, sex,
income, profession, etc. As soon, that is, as statistics goes more
into details, it points to influences of a more special kind, de-
pending upon the special nature of the state of society in that
particular circle of the community. Still the utmost that
statistics could do, — and this will really never be possible for it
for many reasons, — would be to follow its investigations out till
it reached such circles as stood in all external respects under
identical influences, circles the age, sex, profession, etc., of whose
members were absolutely similar. Statistics would furnish us
with regular figures for the voluntary actions even of these
narrowest circles, and we could calculate from them the force,

43 2 Lectures on Human and Animal Psychology

as it were, with which each individual is attracted to a particular
voluntary action by the conditions under which he lives. But
so long as there remain individuals who resist this force we
shall be obliged to take into account a personal factor if we are
to understand the causality of the particular voluntary action.

§ IV

The determinants of volition which have their source in the
social condition of a people, and the existence of which is de-
monstrated by statistics, come within the causal nexus of
natural and historical processes. They serve, then, to prove
once and for all that the will is not undetermined. But statistics
can do no more than discover the external causes of voluntary
action ; as to its internal causes, we are left wholly in the dark.
•* These internal causes constitute the personal factor, which from
its very nature must elude any statistical observation. Whether
it operates by way of cause and effect, and if so what the form
of this causation is, are questions which the rough averages of
statistical examination cannot of course decide.

This personal factor conflicts in various ways with the other
factors determining volition. Thus the general will furnishes a
reason for the determination of the individual will, but it re-
mains for the personal factor to decide whether the result aimed
at by the general will shall also be the object of the volition of
the individual. In the same way a determining influence is
continually exercised by the state of society in the whole com-
munity and in the professional circle to which the individual
belongs ; but here again the separate act of will is never per-
formed without the decisive co-operation of the personal factor.

Now what is this personal factor, which of all the determi-
nants of volition proves to be so indispensable ? When we have
taken account of every one of the external reasons that go to
determine action, we still find the will undetermined. We must
therefore term these external conditions not causes, but motives,
of volition. And between cause and motive there is a very
great difference. A cause necessarily produces its effect ; not
so a motive. A cause may, it is true, be rendered ineffective, or
its effect be changed, by the presence of a second and contrary
cause, but even then the result shows the traces of it, and that

Character as the Ultimate Cause of Wilt 433

in measurable form. But a motive may either determine
volition or not determine it; and if the latter is the case,' then
exerts no demonstrable effect.

The uncertainty of the connection of motive and volition is
due, and due only, to the existence of the personal factor. In
consequence of this, all motives are seen to be insufficient for
the complete explanation of a voluntary action ; they can never
be constraining causes, but remain as partial determinants.
And the motives of volition are insufficient for its explanation,
simply because the nature of the personal factor itself and the
manner of its co-operation with external factors are wholly un-
known. At the same time the fact that an ineffectual motive
leaves no trace upon the completed volition points towards the
inference that external motive and internal factor do not co-
operate as does a plurality of causes in nature, but that per-
sonality is the only immediate cause of action, i.e.t that the only
direct effect of a motive is exerted upon the personality..
Properly speaking, therefore, we may not talk of a ' personal
factor,' since that expression implies the simultaneous co-opera-
tion of other factors. Rather, since all the immediate causes of
voluntary action proceed from personality, we must look for the
origin of volition in the inmost nature of personality, — in
character.

Character is the sole immediate cause of voluntary actions.
Motives are only mediate causes of them. Between the moti-
visation and the causality of character there is this essential
difference, — that motives are immediately given or are at least
determinable by a close examination of the external conditions
of an action, while the ultimate grounds of causation remain
unknown to us, opening out as they do into the infinite series
of the psychological conditions of the development of the
individual mind.

We estimate a man according to the reaction of his character
to external motives. That is, we judge of his character from
his voluntary actions ; we determine character from its effects,
and can never define it in any other way than by reference to
these effects. The real nature of personality, therefore, is
always a riddle. Now, whenever we come to the limits of our
solution of the problems of philosophy, there remains the final

F F

434 Lectures on Hitman and Animal Psychology

problem, a riddle which we cannot read. But in this case the
knotty point seems to lie clearly before us in the midst of a
series of cognisable causes and effects. The motives which
determine the will are parts of the universal chain of natural
causation. Nevertheless, the personal character, which alone
can constitute volition, cannot be assigned a place in this causal
nexus. We cannot therefore decide immediately and empiri-
cally that personality in its inmost nature, the source and origin
of every difference that exists between individuals and between
communities, is itself subject to natural causality.

It has been said that a man's character is a resultant of air
and light, nurture and climate, education and destiny ; that it is
predetermined by all these influences, like any other natural
phenomenon. The assertion is undemonstrable. Character
'itself helps to determine education and destiny ; the hypothesis
makes an effect of what is to some extent also a cause. And the
facts of psychological inheritance make it extremely probable
that if our investigation could penetrate to the very beginnings
of the individual life, we should find there the nucleus of an
independent personality, not determinable from without, because
prior to all external determination.

On the other hand, it is equally impossible to prove by an
appeal to experience that character is not a product of the
external influences at work to form it. Would two men the
course of whose whole lives was absolutely identical show
precisely the same peculiarities of character ? We cannot say ;
the case has never been realised in experience. So far as the
deficiencies in experience admit of any answer at all being re-
turned to the question, we should conjecture that the truth lay
somewhere between the two extremes : character is partly the
result of conditions of life, partly an original possession of the
personality. But the further question of the causality of cha-
racter is not settled by that answer, for the beginnings of it, not
caused in the individual life, may still be terms in some more
universal causal nexus.

However that may be, personal character is the ultimate cause

V of volition. And this statement contains the immediate answer

to another question, a question which can be met independently

of any dispute as to the freedom of the will, — whether, namely,

Character as the Ultimate Cause of Will 435

the individual is responsible for his actions or not. Punishment
cannot, is not intended to, affect the external occasion of a
crime, but the criminal, i.e., the criminal character, as acting of
its own initiative, in terms of its own causation. This character,
you see, is placed in a more or less external community, and
finds there a causality which is foreign to it. But, to estimate
adequately the right of punishing it, we must look at the whole
matter from the point of view of this wider community. Surely
it must be conceded to every society as an inalienable right
that it may defend itself against the attacks of its own members.
For the general will stands in this respect above the individual
just as unconditionally as the latter stands above the organs
which obey the behests of the personal self.

The individual, then, brings with him into the world the germ
of his future character. Two hypotheses are possible for the
explanation of the existence and nature of this original endow-
ment : we may say the germ of character in every individual
is a special creation, or we may regard it as a resultant of the
conditions embodied in previous generations. Our choice be-
tween these alternatives will be determined by our general
metaphysical theory. If we look upon every form of life as an
original creation, we shall find no difficulty in supposing that
the birth of the individual involves a creative act, producing
this or that bodily or mental force from nothing. If we believe
in a developmental continuity, we shall choose the second path.
There can be no doubt that the very earliest developmental
stages of the individual contain in them rudiments of all his
bodily and mental capacities. But we can neither demonstrate
with certainty what the contents of these rudiments is, nor
tabulate with any completeness the influences that come to
work in the course of the individual life. What principally in-
clines us to admit no gap in the chain of processes connecting
the special constitution of the individual with the general nature
of the community into which he is born is the realisation of our
endeavour to obtain a single theory applicable alike to the
mentality of the individual and of society. If personal character
grows out of a causal nexus extending far beyond personal
existence, the determination of volition must also be sought
outside of and beyond the individual life, and will prove incal-

436 Lectures on Human and Animal Psychology

culable from the factors which influence it. Every cause that
stands behind the existence of the individual is itself the out-
growth of a still more remote chain of causation, and to follow
this link by link to the end would be to trace out the causality
of the universe. Herein is to be found the justification for the
view of religion which in its symbolic way makes will the gift
of God.

But if character, takes its origin in a causal nexus that ex-
tends beyond the individual life, it follows that the innermost
causation of volition not only is unknown, but must necessarily
remain unknown. And this gives us the distinction between
•volition and chance, which determinism is so fond of comparing
Chance depends on a defect of our knowledge which can pos-
sibly be made up ; volition depends upon a necessary and
irremediable defect of knowledge. That is why we are so apt
to regard a chance occurrence in external nature as only an
apparent exception to the causal law, while we look on volition
as an actual exception. The real reason for this difference is
just what we have been saying, — that character, of which every
voluntary act is an expression, has its origin outside of and be-
yond the individual life and consciousness, in the infinite con-
tinuum of mental development. The more complete the
determination of character by personal experience, the greater
is the confidence of our prediction that it will act so or so in a
particular case. So it happens that the more the will matures,
the farther it travels from its original inherent determination,
the more certain does its direction become, and the closer the
approximation of its external manifestations to a mental series
necessarily and causally related.

LECTURE XXX

§ I. CONCLUDING REMARKS; THE QUESTION OF IMMORTALITY. § II.
THE PRINCIPLE OF PSYCHOPHYSICAL PARALLELISM. § III. OLD
AND NEW PHRENOLOGY. § IV. THE EMPIRICAL SIGNIFICANCE
OF THE PRINCIPLE OF PARALLELISM. § V. THE NATURE OF
MIND.

§1

AT the beginning of these lectures upon the mental life of
man and the animals we declined to base our considera-
tions from the outset upon any hard and fast conception
of the nature of mind, and to force the facts ot experience into
agreement with that conception, in the way of the metaphysical
psychologists. On the contrary, we regarded it as our primary
duty to acquaint ourselves with the facts, and then, without the
aid of any other assumptions than those suggested by intro-
spection and supported by experimentation and objective
observation, to try and establish laws under which the phe-
nomena of mind might be subsumed.

But, now that we have come to the end of our task, it becomes
imperative for us to cast a glance over the body of facts that
we have collected, and to consider what answer is co be given
to the ultimate questions of psychology. The path that we
have travelled was not lighted by any metaphysical guiding
star. What is the result ? Do these questions refuse to be
answered ? do they transcend the limits of human knowledge ?
Or has experimental psychology something to say about them,
something which may be believed and accepted as the issue of
an unprejudiced appeal to experience ?

There is, indeed, one problem of speculative psychology which
we must exclude from the first as insoluble. Not only does it
transcend the limits of the empirical doctrine of mind : it does
not stand upon the plane of scientific knowledge at all. It is

438 Lectures on Human and Animal Psychology

the question of the condition of the mind before or after this
conscious life of ours, a question which has really as little place
in psychology as that of the ' creation ' of the world has in
physics or astronomy. The hope of constructing from the
materials of our knowledge of the universe a conceptual edifice
in which the objects of a supersensuous world are transformed
into objects of knowledge, — that hope has always and again
proved to be one of those fatal illusions from which neither
belief nor knowledge has anything to gain.

If you need confirmation of this, look for a moment at the
question of immortality, one of the principal problems of
metaphysical psychology. It was necessary to put the im-
perishability of the individual mind beyond all doubt. That
necessitated the continual emphasising of its substantial sim-
plicity. And that led in the last instance to the logical extreme
of the Herbartian metaphysic, in which we have a mental atom
of simple quality with an unalterable content comparable, —
these are Herbart's own words, — to a simple sensational quality,
like 'blue' or 'red.' How does the imperishability of this mind-
substance differ from, say, the imperishability of a material
atom ? Is it anything better ?

The one aim of empirical psychology is to explain the inter-
connection of the phenomena of our mental life. It must
decline once and for all to furnish any information regarding
a supersensuous mental existence. At the same time, the
question may with some right be raised whether it is not at
least indirectly concerned in this problem. We cannot deny
to philosophy either the privilege or the duty of passing beyond
the mere explanation of facts of actual life, on the basis of the
total sum of knowledge amassed by the several sciences. The
actual character of the world-process renders it inevitable that
the solution of this our first problem should be followed by the
presentation of a second. Facts are given us in the form of
continuous developmental series which in experience terminate
at this point or that. Philosophy must go beyond experience,
and strive to attain the ideal goal of all science, — a coherent
theory of the universe. Now our mental life in particular is
presented in the form of a whole number of developmental
series, all directly or indirectly interconnected and all together

The Question of Immortality , 439

tending towards the same end, which, indeed, is inaccessible to
our immediate experience, but the nature of which we may
infer, if we are allowed to assume that the developments begin-
ing in experience are continued on the same lines beyond the
bounds of experience. It is the aim of philosophy to supplement
the world of experience in this way. In doing so she is only
carrying to its logical conclusion a method of procedure which
is begun in every one of the separate sciences, and which is
rendered necessary both by the character of the experiential
developments and the impulse to fill out incomplete systems of
knowledge. Now the mental life of the individual stands at
the centre of this plurality of mental developments. The
individual, with all his actions and impulses, is placed in mental
communities of wide and of narrow radius. As a member of
such communities, he contributes his share in the last resort to
the sum of the achievements and creations of the human mind.
What is the ultimate goal of all this mighty current of mental
development ? Experience alone cannot answer ; while the
ideal completion of experience, which philosophy tries to dis-
cover, can have no other foundations than the developments
given in experience. It is here that psychology finds a place ; it
is one of the first witnesses called upon by philosophy for infor-
mation which shall aid in her ideal construction. And this must
never be opposed at any point to established psychological fact.
Now, if we recognise the existence of this problem of an ideal
completion of reality, we have also recognised a continuance of
mentality in the widest sense, — i.e., a persistence of the mental
developments beyond every experiential limit wherever and
whenever attained. For the hypothesis that mental develop-
ment might somewhere come to an end, to be replaced by
simply nothing, would, of course, imply a recognition of the
invalidity of any ideal completion. More than that, the whole
of the mental content of the universe would cease to have any
significance. For what meaning could we read into mental life
in general other than that of a great and lamentable illusion,
the growing store of man's mental possessions confirming him
more and more strongly in his justifiable expectation of further
development, while the end of all things should still be nothing-
ness ?

440 -Lectures on Human and Animal Psychology

There can be no doubt that it was this philosophical notion
of purposiveness, and not any particular speculation as to the
nature of the individual mind, which ultimately gave rise to
the idea of immortality, and has empowered it to resist
throughout all times the attacks of philosophic doubt and the
force of opposing philosophic argument. But mankind inclines
to look at things sub specie individualitatis rather than sub
specie ceternitatis, and has therefore transformed this general
conviction of the imperishability of mental development into a
belief in the imperishability of each individual mind, with all
its sensuous contents, — a contents that could only have been
acquired under the special conditions of this present sensuous
life.

Psychology proves that not only our sense-perceptions, but
the memorial images that renew them, depend for their origin
upon the functioning of the organs of sense and movement, of
the nervous system, and ultimately of the total mechanism of
the living body. A continuance of this sensuous consciousness
must appear to her irreconcilable with the facts of her own
experience. And surely we may well doubt whether such a
continuance is an ethical requisite : more, whether the fulfilment
of a wish for it, if possible, were not an intolerable destiny.
But when we turn away from this, the idea of immortality
in a bygone mythology, and return to its true philosophic
foundation, empirical psychology has nothing to urge against
it. For the mental development of the individual is a necessary
constituent of the development of the universal mind, and
points not less unequivocally than this to something lying
beyond it.

§ II

Besides this first question, which has taken us from psychology
into philosophy, and into the most difficult and uncertain part
of philosophy, there are two others of general import to which
we may be required to give a final answer on the basis of the
facts which we have been discussing. The first is that of the
relation of mental to bodily processes ; the second, that of the
nature of mind, as inferable from our survey of the whole range
of mental experience. Our only way to furnish an answer to

The Principle of Psyckophysicat Parallelism 44 r

either is, of course, to put together the results of our various
investigations.

We emphasised the fact, at the very beginning of these
lectures, that mental phenomena could not be referred to bodily
as effect to cause. It is an inevitable presupposition of the
natural sciences that the processes of nature constitute a straitly
closed circle of movements of unchangeable elements, governed
by the general laws of mechanics. Nothing can ever be derived
from motion except another motion. In other words, the circle
of these natural processes which are presented to our objec-
tive observation can never lead to anything beyond itself
Recognising this, we recognised the necessity of deriving eve/-
mental process from some other, the more complicated from
the simpler, and of making it our business as psychologists to
discover the mental laws of this interconnection. And at every
stage upon the road which we have travelled we have found
confirmation of this general position. Every well-established
case of a connexion of mental phenomena has proved capable
of a psychological interpretation ; more, we have always seen
that no other interpretatory method could throw light on the
specifically psychological character of the process under in-
vestigation. Thus the fundamental law of the doctrine of
sensation, Weber's law, was shown to be a mathematical ex-
pression of the principle of relativity of mental states. And
the different modes of ideational connection in sense-perception
and in the temporal and spatial combinations of memorial
images were referable to the laws of association, which them-
selves, when analysed into the two elementary processes of
connexion by likeness and connexion by contiguity, appeared
as directly dependent upon psychological conditions. Further,
the laws of apperception, with their corollaries of the com-
position and disintegration of general ideas which underlie
the intellectual processes, are only capable of psychological
interpretation. Finally, the feelings, with their classification, —
again, only psychologically intelligible, — as pleasurable and
unpleasurable mental reactions, and the excitations of volition,
took their places as terms in a developmental series, extending
from the simplest forms of impulse to the most complicated
expressions of self-initiated, voluntary activity. It may very

442 Lectures on Human and Animal Psychology

well be that we have not yet discovered the simplest and best
formulation for many of these causal connexions ; and it cannot
be doubted that many important laws of mental life still
await discovery. But neither does it admit of any doubt that
psychical can only be adequately explained from psychical,
just as motion can only be derived from motion, and never from
a mental process, of whatever kind.

At the same time, we found it to be a truth of equal uni-
versality that mental processes are connected with definite
physical processes within the body, and especially in the brain ;
there is a uniform co-ordination of the two. How are we to
conceive of this connexion, if, as we have stated to be the case,
it is not to be thought as that of cause and effect ? The answer
to this question has been given in detail in the preceding
pages of the book. The connexion can only be regarded as a
parallelism of two causal series existing side by side, but never
directly interfering with each other in virtue of the incompara-
bility of their terms. Wherever we have met with this principle,
we have named it that o>i psychophysical parallelism. Its validity
cannot be doubted even by those who may be of the opinion
that there may still perhaps be some metaphysical bridge to
take them from physical to psychical, or vice versa. Even they
must admit that it is the most obvious empirical expression of
the connexion which we actually found to obtain between the
bodily and mental series of vital processes. But the question
of the extent of the validity of the principle is a different
matter. It requires further consideration ; and only at the
conclusion of this shall we be able to hazard a conjecture as to
whether we are dealing with an ultimate principle of dualistic
metaphysics, beyond which our knowledge cannot go, or
whether the psychophysical facts which we have co-ordinated
tend at all to justify the philosophical attempt to fuse these two
parallel and independent causal series in the last resort in a
higher metaphysical unity.

The question of the extent of the validity of this principle
of psychophysical parallelism can be approached either from
the physical or mental side. From the former point of view,
our direct experience of the parallelism tells us in plain terms
enough that its range is exceedingly limited. Of the whole

The Principle of Psychophysical Parallelism 443

number of physical processes, which constitute the course of
the material universe, vital phenomena form but a narrow
and circumscribed part ; and of vital phenomena themselves
there are again but few in which mental processes can either
be perceived or inferred from objective observation. This is
undoubtedly one of the principal reasons upon which is based
the materialistic view that psychophysical parallelism itself
formulates a causal dependence of the mental upon the physical.
Regarded as systems of processes in nature, the physical is "•"
wider than the psychical ; mind is bound up with certain
definite connexions and attributes of matter. And so it seems
an obvious assumption that mental activities are functions of
certain highly organised substances. But such statements do
not meet the requirements of a really causal explanation. It is
surely inadmissible to suppose that mental existence suddenly
appeared at some definite point in the developmental chrono-
logy of life. It is a far more justifiable hypothesis that that
point merely serves to mark in a general way the limen of a
more clearly conscious mental life. An isolated sensation, out
of all connexion with other sensations or ideas, could not make
itself known to us, whether subjectively or objectively, by any
symptoms of consciousness. But since our analysis of ideas
takes us back to sensations as their ultimate elements, we have
every right to assume that primitive mentality was a state of
simple feeling and sensing ; while the possibility that this state
accompanies every material movement-process, — that is to say, v
that the principle of psychological parallelism, even when re-
garded from the physical side, is of universal validity, — though,
like every ultimate assumption, incapable of proof, is still
certainly not to be denied. At least, it looks very much more
probable than the materialistic function-hypothesis, if we accept
the dictum ' Ex nihilo nihil fit.' That the beginnings of mental
life are to be found in the vegetable kingdom, and particularly
in the protozoa, whose life represents the earliest stages of de-
velopment both of plants and animals, is a theory, it is true ;
but it is the only theory which can explain the phenomena of
movement displayed by these primitive creatures.

If, on the other hand, we prefer to consider the principle of
psychophysical parallelism from its second or mental side, we

444 Lectures on Human and Animal Psychology

again find ourselves in some doubt as to the extent of the
connexion between mind and body. The older spiritualistic
psychology was inclined upon the whole to restrict it to sense-
perceptions and external voluntary actions, — processes whose
relation to physiological conditions could not well be over-
looked. But in more recent times there has sprung up a
tendency both in physiology and in psychology to look upon
a considerable extension of the sphere of psychophysics as
right and necessary. Every conscious content which possesses
sensible attributes of whatever kind, — i.e., which is to some extent
constituted by sensations, however slight their intensity, — must
be recognised at once as a psychical content with a physical
substrate. There is, as you know, no certain characteristic by
which to discriminate the sensational content of a memorial or
fancy image from that of a sense-perception. The ordinary
one, that of the different intensity of the sensations, does not
furnish a valid criterion ; for the intensity of a peripherally
stimulated sensation may be just as near the limen of notice-
ability as that of a memorial image, while the strength of the
latter, when it takes the form of a hallucination or an illusion,
may rival that of any externally excited sensation. Since,
moreover, as we have seen, the intensity of sensation stands in
a uniform relation to the intensity of the physical excitation,
there is not the slightest reason to suppose that the difference
between memory-image and sense-perception consists on the
physiological side in anything more than a difference in the
intensity of the underlying excitation-processes.

But if all the mental processes whose contents involves the
presence of sensation in any form may be thus subsumed to
the principle of psychophysical parallelism, it becomes im-
possible to make an exception in favour of the intellectual
processes. Every concept requires an idea to serve as its
symbol in consciousness ; and an idea without sensational con-
tents is an absurdity. Conceptual thought will, therefore, be
accompanied by an excitation-process in certain sensory centres.
If thought is engaged upon the composition or analysis of
concepts, there will always be effected an alteration in the
contents of these, i.e., in the sensational contents of their repre-
sentative ideas. Corresponding to every process of thought

Old ^and New Phrenology 445

there will be some physical excitation, varying with the
variation of sensational elements. And we can go even farther.
The apperception of an idea, the strain of attention upon an
idea, is always attended by changes in the sensational content
of that idea. Sharp as is the general distinction between the
clearness or obscurity of an idea on the one hand and its
strength or weakness on the other, still both alike depend upon
the greater or less noticeability of its sensational constituents
and attributes. So that if sensations themselves are accom-
panied by physical processes, the alterations in ideas connected
with alterations in certain of their constituent sensations will
also be accompanied by them. In the case of strained atten-
tion we must add to these alterations the associated muscle-
sensations, which must, of course, follow the rule governing
sensation in general. And, finally, if the apperception of ideas
can be subsumed to the parallelistic principle, we must recognise
that its intimate relation to volition cannot but involve the
internal impulses of will in the same fate. Every volition as
well implies an alteration in the ideational, — i.e., also in the
sensational, — contents of consciousness. So that the physical
processes which attend the external voluntary movement are
only a further expression of a relation in which the will has
stood from the time of its very first beginnings.

§ HI

The result of all these considerations, then, is to make it
exceedingly probable that no mental process which contains
sensational elements of any kind can occur without there being
at the same time set up corresponding physical processes. The
universal validity of the principle of psychophysical parallelism
is given with the sensible nature of the foundations upon which
our whole mental life rests. There is no concept so abstract,
no notion so remote from the world of sense, that it must not
be represented in thought by some kind of sensible idea, But
it would for this very reason be wrong to regard this parallel-
ism as though it implied an equivalence of the two series of
processes. Physical and psychical are, as you know, wholly
incomparable. And they differ more especially in this point, —
that the criterion of value which is the ultimate standard of

446 Lectures on Human and Animal Psychology

reference both for those of our conscious activities which affect
the world outside us, and even to a greater degree for our
appreciation of the phenomena of consciousness itself, is wholly
inapplicable to physical processes, or, at least, can only be
applied where they can be derived from some mental purpose,
i.e., are subsumed to the psychological point of view. Regarded
as such, considered simply from the standpoint of natural
science, every physical process is a link in the unbroken chain
of movement-processes, of as much or as little value as any
other link. A memorial image may hurry through conscious-
ness as the transient reproduction of some past experience to
which we are utterly indifferent ; or it may serve as a vicarious
idea to embody a concept which expresses an important result
of logical reflection. Within the circle of physical processes
there will occur in both cases the same weak sense-excitation,
connected, if you will, with very different antecedent and con-
sequent motions, but giving not the least sign of the difference
in mental value which attaches to it. If we could see every
wheel in the physical mechanism whose working the mental
processes are accompanying, we should still find no more than
a chain of movements showing no trace whatsoever of their
significance for mind. So that, despite the universality of the
parallelistic principle, all that is valuable in our mental life still
falls to the psychical side. And the fact of parallelism can
affect this value just as little as the necessity of embodying an
idea in a word or some other sensible symbol, if it is to be a
permanent property of thought, or even thought at all, affects
the value of the idea itself. The value of a work of art of im-
perishable beauty does not depend upon the material of which
it is made. The material only becomes valuable because
capable of giving expression to the conception of the artist.
And it is only carrying this relation of mental conception to
its objective realisation one step farther back to apply it to
the less durable, but therefore all the more plastic, material of
ideation, upon the varying content of which consciousness has
to work. The artist could not call his thought to life in stone
or bronze, in word or picture, if it had not already gained the
potentiality of that life in his own mind as a work of the
constructive imagination from the sensible material of ideas.

Old and New Phrenology 447

It need now hardly be said, that psychophysical parallelism is
a principle whose application extends only to the elementary
mental processes, to which definite movement-processes run
parallel, not to the more complicated products of our mental
life, the sensible material of which has been formed and shaped
in consciousness, nor to the general intellectual powers which
are the necessary presupposition of those products. Phrenology,
as you may know, localised memory, imagination, understanding,
and even such narrowly defined faculties as memory for things
or words, sense of colour, love of children, and so forth, in
particular parts of the brain. It assumed that the physical pro-
cesses in those parts, — and it left their physiological character
altogether undetermined, — run parallel to these complicated
mental capacities and activities. These are the ideas of the
crudest forms of materialism, and render any psychological
understanding of our mental life altogether impossible.

The absurdity of the phrenological hypothesis is not greatly
diminished in the more modern form of it. Starting out from
the facts of cerebral localisation, it assumes that each single
idea is deposited in some particular nerve-cell ; so that the
excitation of this cell is synchronous with the appearance of its
special idea. We can only account for such notions by sup-
posing that observers who had absorbed the false doctrines of
the older phrenology, when they came into contact with the
modern discoveries of the histology and minute anatomy of the
brain, felt it their duty to transfer the phrenological functions of
lobe and convolution to the more elemental cell. To do this,
it was necessary to get rid of memory, imagination, linguistic
talent, etc., and to endow the morphological units with the
separate ideas of which the complex mental faculties are con-
stituted. Now we have seen how complicated, as a rule, those
mental processes are which terminate in the formation of an
idea, how many sensations taken from the most various de-
partments of sense may be involved in them. It is impossible
to suppose that the structural elements of the brain can be
related to mental processes in any way differently from the
structural elements of the external sense-organs. Each such
element is adequate only to a very simple function ; but it can
play a part in the most diverse and complicated functions. A

448 Lectures on Human and Animal Psychology

single cell from the visual area of the cortex can no more be
the seat of a definite idea, — say, of a house or of the face of a
friend, — than can a single retinal rod or opticus fibril. The
phrenological view has only to be carried to its logical extreme
for its impossibility to become manifest. Suppose that we
are in daily intercourse with a friend ; that we have seen him
in numberless situations. We must assume that he takes up
not one cell, but a whole number of cells, in our brain. If our
next meeting with him takes place under ordinary circumstances,
we can use one of our stock of ideas ; if not, — if he has a new
hat on, perhaps, — this new idea will have to be stored away in
some cell that happens to be empty at the time. Or suppose
that we have learned a word of a foreign language. It is
deposited in some cell of the central organ of speech. If we
hear the same word with some slight change of pronunciation,
this modified form must be laid up in a second cell, and so
ad infinitum. It is evident at the first glance that the hypo-
thesis of idea-cells gives no account of the manifold forms of
ideational and sensational connexion. It would fall to pieces
at the first attempt from the inherent impossibility of its effort.
For, as a matter of fact, it is never ready-made and isolated
ideas that combine, but ideational elements, or, better, element-
ary ideational processes, as we saw when analysing out the
simple associative processes underlying the cognition and re-
cognition of an object. The radical error of the phrenological
hypothesis is, that it substitutes an anatomical for a physiological
parallelism. It is a true scion of the old-time phrenological
doctrines in this as well as in its extraordinarily naive notions
about psychology in general.1

§ IV

The principle of psychophysical parallelism, then, refers always
to a parallelism of elementary physical and psychical processes,
and not to any parallelism of complex activities on either side
or of mental function and bodily structure But this suggests

1 For other proofs of the untenable character of the neo-phrenological
localisation-hypothesis, drawn chiefly from the phenomena of normal and
pathological disturbances of memory, I may refer the reader to my Essays,
pp. 109 ff. (Leipzig, 1885).

The Empirical Significance of Parallelism- 449

a further question, — whether a principle which after all includes
two utterly disparate principles, disparate and yet never out
of relation to each other, can properly be regarded as an
ultimate psychological postulate. Is not a dualistic principle
like this in opposition to our justifiable endeavour after a
monistic world-theory ? And if we cannot doubt its validity,
since psychological and physiological facts alike attest it, should
we not still, perhaps, look upon it as provisional only ?

Certainly we have reached the point where psychological
assistance can avail us no more, and where we must appeal to
metaphysics for an answer. It is, or it should be, the aim of
metaphysics to satisfy this craving of the reason for final uni-
fication. The results gained in the separate spheres of scientific
investigation are unable to do this. If, then, there is anything
at all for metaphysics to do, it is to furnish the ultimate ex-
planation of this parallelism, which physiology and psychology
accept as bare fact. Physiology cannot be called on for this
explanation. It restricts itself to the explanation of the phy-
sical manifestations of life ; and though often and again it comes
upon the signs of mental function, it is obliged to consider this
as a department of knowledge with which it has no concern.
The problem of pyschology, again, is the explanation of the
interconnection of the psychical manifestations of life, which
form another and a separate causal series. But the two sciences
supplement each other ; where certain links are wanting in the
causal nexus of the one side, they may be given in that of the
other. In these cases, of course, physiology must have re-
course to psychological, psychology to physiological, connecting
terms. But it is always understood that the interpolation does
not carry with it any real completion of the broken chain of
connected processes ; it is simply the substitution for a term of
one series of the parallel term of the other. We may speak
in such instances, perhaps, of the influence of mind upon body,
or vice versd. But we always mean, if we do not say, that the
word ' influence ' is not to be taken sensu stricto : that, for in-
stance, a direct causal influence cannot be exerted by psychical
term upon physical, but only upon the psychical process which
this physical represents by parallelism. Thus an external
voluntary movement is not produced by the internal act of will,

G G

45° Lectures on Hitman and Animal Psychology

but by the cerebral processes correlated with it ; an idea docs
not follow from the physiological excitations of the sensory-
centre, but from the processes, sensational and associative,
which run parallel to them. We must even suppose, continu-
ing this train of reasoning, that it is not the physical stimulus
which occasions the sensation ; but that this latter arises from
some elementary psychical processes, lying below the limen of
consciousness and connecting our mental life with some more
general complex of elementary psychical processes in the
world outside us. But since we are utterly ignorant of all that
belongs to these, we have no choice : at the beginning of the
development of the empirical mental life, we must substitute a
physiological first term for the psychological. But is psychology
here so much worse off than physiology ? Will it ever be able
to demonstrate the physiological processes which correspond to
the highest productions of psychical life ?

In all its empirical investigations, then, psychology is obliged
to take up the same position as regards the links in the chain
of physiological causality as physiology must assume with
regard to psychological phenomena. The severance of the
spheres of the two sciences must, to be fruitful, go hand in
hand with mutual recognition of these spheres. The only views
of the nature of the bodily processes which are possible for
psychology are, therefore, those current in physiology and the
other natural sciences : it must assume an actually presented,
absolutely constant, material substrate, unalterable save as
regards the movements of its parts. Over against this stands
the circle of the psychical phenomena of life, an equally in-
dependent sphere of investigation, not admitting of causal
explanation in terms of the connection of motions of matter.
So for psychology, as for physiology, the principle of psycho-
physical parallelism turns out to be an ultimate postulate, behind
which it cannot go.

The attitude of metaphysics in this matter is, of course, a
quite different one. The very nature of the objects with which
psychology and natural science alike begin their analysis fur-
nishes it with a sufficient reason for the inquiry after a higher
unity in which the dualism of the parallelistic principle may be
resolved. All that we know of the phenomena of nature comes

The Nature of Mind 45 1

to us in the form of ideas. The distinction of idea and object,
upon which the division of the experiential sciences into those
of nature and mind depends, is simply a result of the analytic
activity of thought. In itself the idea is at the same time
object ; there are no objects which are not also ideas, or which
must not be thought of in accordance with the laws governing
the formation of ideas. But if it is thought which, by abstract-
ing and distinguishing, has broken up the original unity of the
worlds without and within, you can easily understand the
mind's persistent impulse to restore that unity as the final act
of its own development. Nay more, you will recognise the
endeavour as just, and its fulfilment as a task for science. To
point out means to this end is the business not of psychology,
but of philosophy. Psychology can only indicate the path
which leads to territories beyond her own, ruled by other laws
than those to which her realm is subject.

§ V

These considerations have brought us to the last task which
remains to be performed. We have learned all that we could of
the interconnection of mental phenomena. What now is the
nature of mind 1 The real answer to this question is contained
in all that has been said before. Our mind is nothing else than
the sum of our inner experiences, than our ideation, feeling,
and willing collected together to a unity in consciousness, and
rising in a series of developmental stages to culminate in self-
conscious thought and a will that is morally free. At no point
in our explanation of the interconnection of these inner ex-
periences have we found occasion to apply this attribute of
mentality to anything else than the concrete complex of idea,
feeling, and will. The fiction of a transcendental substance, of
which actual mental content is only the outward manifestation,
a fleeting shadow-picture thrown by the still unknown reality
of the mind, — such a theory misses the essential difference
between the inner and the outer experience, and threatens to
turn to mere empty show all that lends solid value and real
significance to our mental life. Conscious experience is im-
mediate experience. Being immediate, it can never require that

452 Lectures on Human and Animal Psychology

distinction of a substrate, existing independently of our subjec-
tive appreciation, which is rendered necessary in natural science
by its conception of nature as a sum-total of real things pre-
sented to us and persisting independently of us. Our mental
experiences are as they are presented to us. The distinction
between appearance and reality necessary for the apprehension
of the world without, and culminating in the concept of a
material substance as a secondary conceptual hypothesis which
so far seems to do justice to the facts of experience, ceases to
have any meaning when applied to the apprehension of the
thinking subject by himself. You can understand, therefore,
that when we are analysing our internal experiences we are
never met by the contradictions between particular phenomena
which in natural science furnish both incentive and means to
the gradual developing and perfecting of the concept of matter,
a concept which, destined as it is to remain for ever a
hypothesis, can still hope to approximate to the truth by an
infinite number of efforts towards it.

There is just one single group of empirical facts which have
with some show of reason been adduced to prove the necessity
of assuming a mental substrate analogous to material substance,
— the facts of the revival of previous experiences. If we can
call up some past idea, it is urged, it surely follows that some
trace of that idea has remained in the mind during the mean-
time, else its reproduction would not be possible. Now we
have seen, of course, that no idea, that no mental process
whatsoever, can be called up again unchanged. Every re-
membered idea is really a new formation, composed of
numerous elements of various past ideas. Nevertheless, it
might be supposed that these very elements were the ideational
traces left behind in the mind. But it is evident that even in
this form the theory has presuppositions due simply to a trans-
ference of the permanent effects observed in the case of physical
processes to the hypothetical mental substrate, in other words
to an unconscious intermixture of materialistic views. A
physical influence acting upon a body produces some more
or less permanent alterations in it. Thus we have every right
to suppose that a nervous excitation leaves an aftet-effect in
the nervous organs, which is of significance for the physiology

The Natiire of Mind 453

of the processes of practice and revival. Now in the theory of
'traces' these physical analogies are applied without more ado
to the mind. Mind is conceived either as identical with brain,
or as a substance localised somewhere in the brain, resembling
it and other material substances in every essential attribute.
But the physical excitation-process can only leave its after-
effect upon the nerve, because it is itself a process of movement
in or with a permanent substrate. And if mental processes are
not phenomena, but actual immediate experiences, it is very
hard to see how their after-effects can be psychologically con-
ceived, except also in the form of directly presented mental
processes. If we try to imagine an idea as persisting beneath
the limen of consciousness, we can as a matter of fact only think
of it as still an idea, i.e., as the same process as that which it
was so long as we were conscious of it, with the single differ-
ence that it is now no longer conscious. But this implies that
psychological explanation has here reached a limit similar to
that which confronts it in the question as to the ultimate origin
of sensations. It is the limit beyond which one of the two
causal series, — the physical, — can be continued, but where the
other, — the psychical, — must end ; and where the attempt to
push this latter farther must inevitably lead to the thinking of
the psychical in physical, — i.e., material, — terms.

We conclude, then, that the assumption of a mental sub-
stance different from the various manifestations of mental life
involves the unjustifiable transference of a mode of thought
necessary for the investigation of external nature to a sphere in
which it is wholly inapplicable ; it implies a kind of unconscious
materialism. The consequences of this transference follow at
once from its nature ; the true value of our mental life is in
jeopardy. For this value attaches simply and solely to the
actual and concrete processes in mind. What can this ' sub-
stance ' do for us, a substance devoid of will, of feeling, and of
thought, and having no part in the constitution of our person-
ality ? If you answer, as is sometimes done, that it is these
very operations of mind that go to make up its nature, and
that therefore mind cannot be thought or conceived without
them, why, then the position is granted : the real nature of
mind consists in nothing else than our mental life itself. The

454 Lectures on Human and Animal Psychology

notion of ' operation ' as applied to it can only mean, if it has
any admissible meaning at all, that we are able to demonstrate
how certain mental manifestations follow from, are the effects of
the operation of certain other mental manifestations. Physical
causality and psychical causality are polar opposites : the
former implies always the postulate of a material substance ;
the latter never transcends the limits of what is immediately
given in mental experience. ' Substance ' is a metaphysical
surplusage for which psychology has no use. And this accords
with the fundamental character of mental life, which I would
have you always bear in mind. It does not consist in the
connexion of unalterable objects and varying conditions : in all
its phases it is process ; an active, not a passive, existence ;
development, not stagnation. The understanding of the basal
laws of this development is the final goal of psychology.

INDEX.

ACTIVITY, in intellectual processes, 312.

After-images, To8 ff.

Analysis,* 13 ff.

Animal intelligence, 340, 343 ff, 353 ff.

Apperception, 244 f, 252 ff, 312, 367, 445.

— Subjective conditions of, 247 f.
Apperceptive connections, 312 ff.
Aristotle, 3, 88, 100, 283, 295, 341.
Assimilation, 286 ff.

Association, 141 f, 148, 189, 194, 283 ff,

3r9-

- and ideational connection, 308.

— and memory, 284.

— and practice, 404 f.

• by similarity and contiguity, 291

ff, 295 ff.

— Conditions of, 141 f.

— Fundamental forms of, 297 ff.

— General significance of, 362 ff.

• in animals, 347 ff, 350 ff, 353 IT.

— Indirect, 306 f.

— of dissimilars, 141.
• — of similars, 141.

— reaction, 279.

- Simultaneous, 141, 284.

- Successive, 141, 295 ff.
Theory of simultaneous, 290 ff.

— — successive, 304 ff.
Associative comparison, 118.
Attention, 249 f, 269, 318.

Development of, 252 ff.

• Fluctuations of, 256 ff.

— Forms of, 253 f.
Antenrieth, 391.
Automatic movements, 227.
Autosuggestion, 331.

Bacon, 341.

Beats, 70 f.
Bessel, 268.
Blindness, accidental, 161.

— Congenital, 161 ff.
Brewster, 186.
Brightness, 87, 104.

CHARACTER, 435 f.

Choice, 225, 228, 233, 255, 388.

— reaction, 279.
Clang, 67 ff, 74, 213.

— colour, 74.
Cognition, 298.

— and concept, 310.

— in animals, 347 ff.
Colour, 87, 105, 213.

— analysis, 89 ff.

— Antagonistic, 99 £

— blindness, 97.

— Complementary, 91.

— contrast, 114.

— Fundamental, 91 ff, 96 ff, 100.

— mixture, go ff.

— Principal, 99 ff.

— triangle, 96.
Combination tones, 76.
Complication. 285 f.

— pendulum, 270.
Concepts, 309 ff, 444, 446.

— None in animal consciousness

358 ff-
Consciousness, 234 ff, 426.

— Contents of, 239 ff.
- Range of, 258 ff.

Trend of, 232 f, 234.
Contrast, 112 ff.
Copernicus, 10.

Index.

Darwin, 385, 389, 406, .40? f.

Decision, 233.

Descartes, 3, 4, 5.

Desire, 224, 229.

Determinism, 425.

Dichotomic law, of logical thought,

314 ff.

Difference tones, 75.
Discrimination, 237.

— reaction, 279.
Disposition, connate, 406.

Distance and apparent magnitude,

176 ff.

Domestication, by animals, 397, 420.
Dreaming, 323 ff.

EFFORT, 13, 144 f, 153, 224.
Emotion and total feeling, 222, 371 ff.

— in animals, 353, 362.
Emotions of the future, 376 f.
Excitability, 21, 348.
Experimental method, 9 ff, 89.
Expressive movements, 372, 381 ff.

Eye and ear method, 267 ff. ,

Eye measurement, 151.
Eye, muscles of, 154 f.

FALLING screen, for range of conscious-
ness. 241 ff.
Fatigue. 147 f.
Fechncr, 32.
Feelings, 13, 210 ff, 234, 247 f, 262.

— aesthetic feelings, 213, 218 f.

— and idea, 221 f.

— and will, 223 f, 231.

— common feeling, 217 ff. 220, 367.

— conceptual feeling, 310,

— discordant feelings, 219.

— intellectual feelings, 218 f, 378 ff.

— Metaphorical names of, 369.

— Obscurity of, 218.

— of inclination, 411, 420 f.

— oscillatory feelings, 219.

— Quality of, 221.

— recognition feeling, 298 f, 301.

— sense feelings, 213 ff.

— Sensory accompaniments of, 370 f.

— total feelings, 219.

Fichte, 4.

Fusion, 181, 188 f, 195, 285.

Goethe, 88, 100.
Grimm, 281.

HEAVINESS after waking, 337 C

Hegel, 4.

Helvetius, 6.

Herbart, 4, 285, 426, 43$.

Holbach, 6.

Homer, 101.

Huber, 344, 349.

Hypnotism, 328 ff.

— and mysticism, 336.

— and therapeutics, 333 ft'.

— Methods of, 329.

— Stages of, 329.

— Theory of, 337 ff.

IDEAS, 13 ff, 170 ff, 210, 222, 230 f, 309.

— Aggregate, 314 ff.

— boundary lines, influence of, 170 ff.
- Clearness of, 243 ff.

— Distinctness of, 245.

— Explication of, in logical thought,

316.

— Fixed, 322.

— Formation of, 182 ff, 195 ff.

— Innate, 392 f, 399.

— Intensity of, 246.

— of depth, 172 ff, 183 ff, 186 ff, 190 ff.

— — Secondary factors in, 175 f,

— Partial suppression of, in binocular

vision, 205 ff.

— Qualitative change in, 282 f.

— Reproduced, 137.

— Rivalry of, 197 ff.

— Temporal course of, 267 ff.

— Unity of, 204 f, 207.

— Visual, 170 ff.
Ideation, 221.
Illusion, 289, 338.
Imagination, 4, 316, 321.

— None in animals, 357 f.
Immortality, 438 ff.

Impulses, 13, 224, 232, 255, 348 f, 385 ft.

— Animal, 408 ff.

Index.

457

Impulses, connate, 401.

• Mimetic, 398.
Indeterminism, 425.
Inheritance, 405, 408 f.
Instincts, 388 f.

— Acquired, 397 ff.

— and adaptation, 408 f.

- and association, 405.
Connate, 399 ff.

— Development of, 408 ff.
Human, 395 ff.

— — and animal, 406 ff.

— Social, 411.

— Theories of, 389 ff.
Intellectual processes, characteristics of,

3" ff.
Development of, 314 ff.

JUDGMENTS, 310 f.

— none in animal consciousness,

361 f.

"Kant, 4, 425.

LANGUAGE, of the insane, 319 ff.

— None of animals, 362 ff.
Leibniz, 4, 244.

Leonardo da Vinci, 99, 100.

Limen of consciousness, 238, 257, 303.

— of difference, 257.

— of stimulus, 50 ff, 257.
Localisation, 131 f, 138 ff.
Local sign, 168 f.

Logical reflection, in popular psychology,

342, 346 f.
Lotze, 168.
Lubbock, 344 f, 421.
Lustre, 202 ff.

— Theory of, 203.

MARRIAGE, animal, 396, 412 f.

Materialism, 2 ff.

Mechanisation of voluntary movements,

398, 4°3-
Memory, 4. 284. 303^347, 452 f.

— and imagination, 289 £

— Aristotle's kinds of, 295.

— image, 287 ff, 290.

Memory in animals, 356.
Mental derangement, 316 ff.

— faculty, 4.

• process, 166.

- product, 1 66.
Mesmer, 329.

de la Mettrie, 6.

Mimetic movements, 381 ff. 396, 402-

Mind, 2 ff, 437 ff, 451 ff.

Mood, 372 ff.

Motives, 231, 428 ff.

— and character, 433.
Movement, illusions of, 136 ff.

— impulsive movements, 383 f.

— of objects, 172.

— Reflex, see Reflex movements.

— Sensation, see Sensation muscular.

Newton, 89, 91, 92, 102.
Noise, 67, 77 f.

OBJECTS, tridimensional, idea of, 190 ff.
Optical illusions, 156 f, 183.
Overtones, 72.

PATHOLOGY, 97, 125, 136 f, 161 ff, 216,,

316 ff, 323 ft.
Perception, 244 f.
Personal difference, 267 ff, 273.
Photometer, 27.
Phrenology, 445 ff.
Pitch, 67, 78, 81, 213.
Plato, 2 f,
Play, 357 f.
Pliny, 350, 357.
Post-hypnotic, effects, 332.
Practice, 144, 227, 402 ff.
Psychology, aids to, 9.

— and philosophy, 438 ff, 450 f, 454.

— Animal, 340 ff, 353 ff.

— Every-day, errors of, 337 ff.

— " Hypnotism," errors of, 337 ff.

— logic and aesthetics, 316.

— Methods of, 8 ff, 12 ff, 241, 276,

342, 345 f. 422.

— of man and animals, 365 ff.

— Philosophical anticipations of, 2 ff.

— Problem of, i ff, 454.

458

Index.

Psychophysical parallelism, 145, 440 ff.

— — Anatomical form in phreno-

logy, 448.

— — Empirical significance of,

448 ff.
Pythagoreans, 68.

QUETELET, 429.

RAPPORT, 331.

Reaction, muscular and sensorial, 277.

— Simple and compound, 278.

— time, 275 ff.
Recognition, 132, 283 f.

— and association, 302.

— and concept, 311.

— in animals, 347 ff.

— Forms of, 298 ff.
Reflection, optical, 199 ff.
Reflex movements, 120 ff. 384.

— — and will, 225 ff.

Development of, 138 ff.
— Influence of practice on, 144 f.

— — of eye, 127 ff, 132 f, 140, 146 ff.
- — of touch, 126, 132, 139.

— — Purposiveness of, 126 ff, 133,

134 ff, 140 f, 225 ff.
Registration method, 272 ff.
Relativity, law of, 62 f, 119, 264.
Responsibility, 435.
Rhythm, 263 ff, 376 f.
Romanes, 343, 355. 359, 4°7-

Schelling, 4.
Schneider, 407.
Self-consciousness, 250 f.
Self, idea of, 147, 231, 234, 250 f. 253.
Sensation, accompanying apperception
247 f.

— Affective tone of, 212.

— Attributes of, 15.

— Definition of, 15.

— Estimation of intensity, 33 ff.

— Fusion of, 74.

— Incomparability of, from differen

organs, 64.

— in complex processes, 444 f.

— Intensity of, 17 ff.

ensation, just noticeable, 50.

— Local character of, 131 ff, 139,

148, 1 68 f, 190.
Measurement of intensity, 18 ff, 63.

— Muscular, 134 ff, 139, 146 f, 173 f,

215 f.

— — of convergence, 152 f.

— Negative intensities of, 42 ff.

— Noticeable and unnoticeable, 45.

— of pressure, 26 f, 32, 50, 65.

— of sight, 27 ff, 32, 52 ff, 87 ff, 129

ff, 242, 257.

— of sight and sound, relation of, 108.

— of smell, 54, 65, 214 ff.

- of sound, 30 ff, 50 ff, 67 ff.

— of taste, 54, 65 f, 214 f.

— of temperature, 54, 65, 214.

— of touch, 128 f, 214.

— Organic, 216 f.

— Quality of, 64 ff, 67, 87.

— Reflex, 124.

— Reproduced, 137.
Unit of intensity, 17 {.

sense of locality, 350.
Senses, chemical and mechanical, in
Sensibility, 4, 21, 86.
Siren, 67 f.
Sleep-walking, 327 f.
Societies, animal, 396, 414 f.
Somnambulism, 330.
Sound pendulum, 30.
Space perception, 180.

- and association, 148, 194.

— — and eye movement, 149 ff

- Tactual, 157 ff, 161 ff.

— — Theories of, 167 ff.

Visual, 151 ff.
Spencer, 392.
Spiritualism, 3 ff.
Stereoscope, 186 ff.

— Combination of dissimilar images

in, 197 ff, 206, 208.

— — of similar images in, 195 ff.
Stimulus, 137.

External, 16.

— Internal, 16, 56.

Relation to sensation, 17 f, 22 ff.
33 ff> 39 ff.

Index.

459

Stimulus, unit of, 47 f.
Suggestion, 329 ff, 339.
Summation tones, 76.

THOUGHT, place of, in human conscious-
ness, 363, 397.
Titchener, 280.
Tone, 67 ff, 72, 75, 76.

Measurement of differences, 78 ff.
Total feeling, 219 f.

UNCONSCIOUS, 235.
Understanding, 4.
Undertones, 75.
Unity of consciousness, 217, 223.

— of feeling, 217.

' — of volition, 234.

VISION, binocular, 182 ff, 209.

— Qualities of, 107.

— Reinverted, 163 ff.

— Stereoscopic, 190 ff.
- Theory of, 103 ff.

Visual distance, least noticeable, 153 f.
Volition, 13, 137 f, 145, 225, 231, 233,

254 f-

— and chance, 436.

Voluntary action, 226, 228 ff, 233 f, 312.
387, 408, 423 f.

— — and instinct, 396.

— — Statistics of, 429 ft

Weber's law, 32, 35, 83 f, 118, 441.

— — and tones, 83 ff.

— — for light sensations, 27 ff,

32.

— — for muscle sensations, 27,

32.

— — for pressure sensations, 26 f,

32.

— — for sound sensations, 30 ft".

— — Limits of, 56 ff.

— — Mathematical expression of,

39 ff.

— — Physiological interpretation,

59 ff, 85.

— — Psychological interpretation,

61 ff, 83 f.

- Psychophysical interpreta-
tion, 61, 84.
Whcatstone, 182, 186.
Will, 210, 223 ff, 321, 445.

- Activity of, 230.

— and character, 432 ff.

- Causality of, 424 ff.

— Development of, 224 ff.

— Freedom of, 424 ff.
Individual and collective, 427,

428 ff.
Wish, 229.
Wolff, 4-

Young, 96, 97, 98.

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